Microcarrier perfusion culturing methods and uses thereof

ABSTRACT

Provided herein are methods of culturing a mammalian cell and various methods that utilize these culturing methods.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/768,085, filed Feb. 22, 2013, the entire contents of whichare herein incorporated by reference.

TECHNICAL FIELD

This invention relates to methods of molecular biology, cell cultureprocess development, and the manufacture of recombinant proteins.

BACKGROUND

Mammalian cells containing a nucleic acid that encodes a recombinantprotein are often used to produce therapeutically or commerciallyimportant proteins. Although several high throughput (HT) cell culturesystems have been used within the biotechnology industry for fed-batchprocesses for years, no HT model for a perfusion-based cell cultureusing shake flasks and microcarriers is known to exist.

Shake flasks containing microcarriers have been used in short-term batch(non-perfusion) culture processes to produce viral vaccines. The celldensities in these methods of producing viral vaccines were low due tothe shear stress caused by the microcarriers. In addition, the recoveryof the viral products from the culture was difficult.

SUMMARY

The present invention is based, at least in part, on the discovery thatculturing a mammalian cell in the specific manner described hereinresults in a substantially improved viable cell density and recombinantprotein production, and is able to effectively model (e.g., an accuratescale-down model) the recombinant protein production of a larger-scalecontinuous-perfusion bioreactor. Thus, the present specificationincludes methods of culturing a mammalian cell that include: providing ashake flask containing a mammalian cell disposed in a first liquidculture medium, where the first liquid culture medium occupies, e.g.,about 20% to about 30% of the volume of the shake flask, and contains aplurality of microcarriers at a concentration of about 1.0 g/L to about15.0 g/L; incubating the shake flask for a period of time at about 32°C. to about 39° C., e.g., about 32° C. to about 37° C., and with arotary agitation of about 85 revolutions per minute (RPM) to about 125RPM; and after about the first 48 to 96 hours of the period of time,continuously or periodically removing a first volume of the first liquidculture medium and adding to the first liquid culture medium a secondvolume of a second liquid culture medium, where the first and secondvolumes are about equal. Also provided are various methods that utilizethese culturing methods.

Provided herein are methods of culturing a mammalian cell. These methodsinclude: providing a shake flask containing a mammalian cell disposed ina first liquid culture medium, where the first liquid culture mediumoccupies about 20% to about 30% of the volume of the shake flask andcontains a plurality of microcarriers at a concentration of about 1.0g/L to about 15.0 g/L; incubating the shake flask for a period of timeat about 32° C. to about 39° C. and with a rotary agitation of about 85revolutions per minute (RPM) to about 125 RPM; and after about the first48 to 96 hours of the period of time, continuously or periodicallyremoving a first volume of the first liquid culture medium and adding tothe first liquid culture medium a second volume of a second liquidculture medium, where the first and second volumes are about equal. Insome embodiments of any of these methods, the first volume of the firstliquid culture medium is substantially free of the microcarriers. Insome embodiments of any of these methods, the first liquid culturemedium occupies about 25% to about 30% of the volume of the shake flask.In some embodiments of any of these methods, at the beginning of theperiod of time, the first liquid culture medium contains 0.1×10⁶cells/mL to 0.5×10⁶ cells/mL. In some embodiments of any of thesemethods, the mammalian cell is a Chinese hamster ovary (CHO) cell. Insome embodiments of any of these methods, the CHO cell contains anucleic acid encoding a recombinant protein. In some embodiments of anyof these methods, the recombinant protein is an immunoglobulin, anenzyme, a growth factor, a protein fragment, or an engineered protein.In some embodiments of any of these methods, the removing of the firstvolume of the first liquid culture medium and the adding of the secondvolume of the second liquid culture medium is performed simultaneously.In some embodiments of any of these methods, the removing of the firstvolume of the first liquid culture medium and the adding of the secondvolume of the second liquid culture medium is performed continuously. Insome embodiments of any of these methods, the removing of the firstvolume of the first liquid culture medium and the adding of the secondvolume of the second liquid culture medium is performed periodically. Insome embodiments of any of these methods, the first volume of the firstliquid culture medium removed and the second volume of the second liquidculture medium added are increased over time. In some embodiments of anyof these methods, the first liquid culture medium is the same as thesecond liquid culture medium. In some embodiments of any of thesemethods, the first liquid culture medium is different from the secondliquid culture medium. In some embodiments of any of these methods, theshake flask is gas-permeable and has a volume of between about 20 mL toabout 1 L. In some embodiments of any of these methods, the mammaliancell is suspended in about 40 mL to about 80 mL of the first liquidculture medium. In some embodiments of any of these methods, the firstliquid culture medium and/or second liquid culture medium is selectedfrom the group of: a chemically-defined liquid culture medium, aserum-free liquid culture medium, a serum-containing liquid culturemedium, an animal-derived component free liquid culture medium, and aprotein-free medium. In some embodiments of any of these methods, afterabout the first 48 to 96 hours of the period of time, in each 24-hourperiod, the first volume of the first liquid culture medium removed andthe second volume of the second liquid culture medium added is about 30%to about 95% of the volume of the first liquid culture medium. In someembodiments of any of these methods, the agitation is ceased for aperiod of time of at least 30 seconds prior to removing the first volumeof the first liquid culture medium. In some embodiments of any of thesemethods, the plurality of microcarriers has a mean diameter of betweenabout 150 μm to about 800 μm. In some embodiments of any of thesemethods, the plurality of microcarriers contains one or more pores. Insome embodiments of any of these methods, the one or more pores has amean diameter of about 25 μm to about 35 μm. In some embodiments of anyof these methods, the shake flask is incubated at a reactor angle ofabout 25 degrees to about 90 degrees from horizontal, or at an anglethat is about 45 degrees relative to the benchtop or the horizon.

Also provided are methods of culturing a mammalian cell that include:(a) providing a shake flask containing a mammalian cell disposed in afirst liquid culture medium that occupies about 20% to about 30% of thevolume of the shake flask and contains a plurality of microcarriers in aconcentration of about 1.0 g/L to about 15.0 g/L; (b) incubating theshake flask for a first time period at about 35° C. to about 39° C. witha rotary agitation of about 85 revolutions per minute (RPM) to about 125RPM, and after about the first 48 to 96 hours of the first period oftime, in each subsequent 24-hour period, (i) continuously orperiodically removing a first volume of the first liquid culture mediumthat is substantially free of microcarriers from the shake flask, wherethe first volume is about 10% to about 95% of the volume of the firstliquid culture medium; and (ii) adding to the shake flask a secondvolume of a second liquid culture medium, where the first and secondvolumes are about equal; (c) incubating the shake flask after the cellconcentration reaches about target cell density for a second time periodof about 2 days to about 7 days, at about 32° C. to about 39° C. withthe rotary agitation, and in each 24-hour period, performing steps(b)(i) and (b)(ii), where the first and second liquid culture media usedin step (b) are of a substantially different type from those used instep (c); and (d) incubating the shake flask for a third time periodgreater than 2 days, at about 35° C. to about 39° C. with the rotaryagitation, and in each 24-hour period, performing steps (b)(i) and(b)(ii), where the first and second liquid culture media used in step(c) are of the same type as those used in step (d). In some embodimentsof any of these methods, the first liquid culture medium occupies about25% to about 30% of the volume of the shake flask. In some embodimentsof any of these methods, at the beginning of the first period of time,the first liquid culture medium contains 0.1×10⁶ cells/mL to 0.5×10⁶cells/mL. In some embodiments of any of these methods, the mammaliancell is a Chinese hamster ovary (CHO) cell. In some embodiments of anyof these methods, the CHO cell contains a nucleic acid encoding arecombinant protein. In some embodiments of any of these methods, therecombinant protein is a secreted immunoglobulin, a secreted enzyme, asecreted growth factor, a secreted protein fragment, or a secretedengineered protein. In some embodiments of any of these methods, theremoving of the first volume of the first liquid culture medium, and theadding of the second volume of the second liquid culture medium in oneor more of the first time period, the second time period, and the thirdtime period is performed simultaneously. In some embodiments of any ofthese methods, the removing of the first volume of the first liquidculture medium, and the adding of the second volume of the second liquidculture medium in one or more of the first time period, the second timeperiod, and the third time period is performed continuously. In someembodiments of any of these methods, the removing of the first volume ofthe first liquid culture medium, and the adding of the second volume ofthe second liquid culture medium in one of more of the first timeperiod, the second time period, and the third time period is performedperiodically. In some embodiments of any of these methods, the shakeflask is gas-permeable and has a volume of between about 20 mL to about1 L. In some embodiments of any of these methods, the volume of thefirst liquid culture medium is about 40 mL to about 80 mL. In someembodiments of any of these methods, the first liquid culture medium andsecond liquid culture medium used in the first time period isserum-containing liquid culture medium or an animal-derivedcomponent-containing liquid culture medium, and the first liquid culturemedium and the second liquid culture medium used in the second timeperiod and the third time period is a serum-free liquid culture medium,an animal-derived component-free liquid culture medium, or aprotein-free medium. In some embodiments of any of these methods, theagitation is ceased for at least 30 seconds prior to removing the firstvolume of the first liquid culture medium from the shake flask duringone or more of the first time period, the second time period, and thethird time period. In some embodiments of any of these methods, theplurality of microcarriers has a mean diameter of between about 200 μmto about 800 μm. In some embodiments of any of these methods, theplurality of microcarriers contains one or more pores. In someembodiments of any of these methods, the one or more pores has a meandiameter of about 25 μm to about 35 μm. In some embodiments of any ofthese methods, the first volume of the first liquid culture mediumremoved during the third period of time contains a substantial number ofmicrocarriers. In some embodiments of any of these methods, the firstvolume of the first liquid culture medium removed during the thirdperiod of time is substantially free of microcarriers. In someembodiments of any of these methods, the first volume of the firstliquid culture medium removed and the second volume of the second liquidculture medium added in one or more of the first time period, the secondtime period, and the third time period is about 70% of the volume of thefirst liquid culture medium. In some embodiments of any of thesemethods, the shake flask is incubated in one or more of (b), (c), and(c) at a reactor angle of about 25 degrees to about 90 degrees fromhorizontal, or at an angle that is about 45 degrees relative to thebenchtop or the horizon.

Also provided are methods of producing a recombinant protein. Thesemethods include: providing a shake flask containing a mammalian cellcontaining a nucleic acid encoding a recombinant protein disposed in afirst liquid culture medium, where the first liquid culture mediumoccupies about 20% to about 30% of the volume of the shake flask andcontains a plurality of microcarriers at a concentration of about 1.0g/L to about 15.0 g/L; incubating the shake flask for a period of timeat about 32° C. to about 39° C. and with a rotary agitation of about 85revolutions per minute (RPM) to about 125 RPM; and after about the first48 to 96 hours of the period of time, continuously or periodicallyremoving a first volume of the first liquid culture medium and adding tothe first liquid culture medium a second volume of a second liquidculture medium, where the first and second volumes are about equal; andrecovering the recombinant protein from the mammalian cell or from thefirst and/or second liquid culture medium. In some embodiments of any ofthese methods, the recombinant protein is recovered from the mammaliancell. In some embodiments of any of these methods, the recombinantprotein is recovered from the mammalian cell. In some embodiments of anyof these methods, the recombinant protein is recovered from the firstand/or second liquid culture medium. In some embodiments of any of thesemethods, the first volume of the first liquid culture medium removed issubstantially free of microcarriers. In some embodiments of any of thesemethods, the first liquid culture medium occupies about 25% to about 30%of the volume of the shake flask. In some embodiments of any of thesemethods, at the beginning of the period of time, the first liquidculture medium contains 0.1×10⁶ cells/mL to 0.5×10⁶ cells/mL. In someembodiments of any of these methods, the mammalian cell is a Chinesehamster ovary (CHO) cell. In some embodiments of any of these methods,the recombinant protein is an immunoglobulin, an enzyme, a growthfactor, a protein fragment, or an engineered protein. In someembodiments of any of these methods, the recombinant protein is secretedinto the first and/or second liquid culture medium. In some embodimentsof any of these methods, the removing of the first volume of the firstliquid culture medium and the adding of the second volume of the secondliquid culture medium is performed simultaneously. In some embodimentsof any of these methods, the removing of the first volume of the firstliquid culture medium and the adding of the second volume of the secondliquid culture medium is performed continuously. In some embodiments ofany of these methods, the removing of the first volume of the firstliquid culture medium and the adding of the second volume of the secondliquid culture medium is performed periodically. In some embodiments ofany of these methods, the first volume of the first liquid culturemedium removed and the second volume of the second liquid culture mediumadded are increased over time. In some embodiments of any of thesemethods, the first liquid culture medium is the same as the secondliquid culture medium. In some embodiments of any of these method, thefirst liquid culture medium is different from the second liquid culturemedium. In some embodiments of any of these methods, the shake flask isgas-permeable and has a volume of between about 20 mL to about 1 L. Insome embodiments of any of these methods, the mammalian cell issuspended in about 40 mL to about 80 mL of the first liquid culturemedium. In some embodiments of any of these methods, the first liquidculture medium and/or second liquid culture medium is selected from thegroup of: a chemically-defined liquid culture medium, a serum-freeliquid culture medium, a serum-containing liquid culture medium, ananimal-derived component-free liquid culture medium, and a protein-freemedium. In some embodiments of any of these methods, after about thefirst 48 to 96 hours of the period of time, in each 24-hour period, thefirst volume of the first liquid culture medium removed and the secondvolume of the second liquid culture medium added is about 30% to about95% of the volume of the first liquid culture medium. In someembodiments of any of these methods, the agitation is ceased for aperiod of time of at least 30 seconds prior to removing the first volumeof the first liquid culture medium. In some embodiments of any of thesemethods, the plurality of microcarriers has a mean diameter of betweenabout 200 μm to about 800 μm. In some embodiments of any of thesemethods, the plurality of microcarriers contains one or more pores. Insome embodiments of any of these methods, the one or more pores has amean diameter of about 25 μm to about 35 μm. In some embodiments of anyof these methods, the shake flask is incubated at a reactor angle ofabout 25 degrees to about 90 degrees from horizontal, or at an anglethat is about 45 degrees relative to the benchtop or the horizon.

Also provided are methods of producing a recombinant protein thatinclude: (a) providing a shake flask containing a mammalian cellcontaining a nucleic acid encoding a recombinant protein disposed in afirst liquid culture medium, where the first liquid culture mediumoccupies about 20% to about 30% of the volume of the shake flask andcontains a plurality of microcarriers in a concentration of about 1.0g/L to about 15.0 g/L; (b) incubating the shake flask for a first timeperiod at about 35° C. to about 39° C. with a rotary agitation of about85 revolutions per minute (RPM) to about 125 RPM, and after about thefirst 48 hours to 96 hours of the first period of time, in eachsubsequent 24-hour period, (i) continuously or periodically removing afirst volume of the first liquid culture medium that is substantiallyfree of microcarriers from the shake flask, where the first volume isabout 10% to about 95% of the volume of the first liquid culture medium;and (ii) adding to the shake flask a second volume of a second liquidculture medium, where the first and second volumes are about equal; (c)incubating the shake flask after the cell concentration reaches abouttarget cell density for a second time period of about 2 days to about 7days, at about 32° C. to about 39° C. with the rotary agitation, and ineach 24-hour period, performing steps (b)(i) and (b)(ii), where thefirst and second liquid culture media used in step (b) are of asubstantially different type from those used in step (c); (d) incubatingthe shake flask for a third time period greater than 2 days, at about35° C. to about 39° C. with the rotary agitation, and in each 24-hourperiod, performing steps (b)(i) and (b)(ii), where the first and secondliquid culture media used in step (c) are of the same type as those usedin step (d); and (e) recovering the recombinant protein from themammalian cell or the first and/or second liquid culture medium usedduring the first, second, and/or third period of time. In someembodiments of any of these methods, the recombinant protein isrecovered from the mammalian cell. In some embodiments of any of thesemethods, the recombinant protein is recovered from the first and/orsecond liquid culture medium used during one or more of the first,second, and third period of time. In some embodiments of any of thesemethods, the first liquid culture medium occupies about 25% to about 30%of the volume of the shake flask. In some embodiments of any of thesemethods, at the beginning of the first period of time, the first liquidculture medium contains 0.1×10⁶ cells/mL to 0.5×10⁶ cells/mL. In someembodiments of any of these methods, the mammalian cell is a Chinesehamster ovary (CHO) cell. In some embodiments of any of these methods,the recombinant protein is an immunoglobulin, an enzyme, a growthfactor, a protein fragment, or an engineered protein. In someembodiments of any of these methods, the recombinant protein is secretedinto the first and/or second liquid culture medium used during one ormore of the first period of time, the second period of time, and thethird period of time. In some embodiments of any of these methods, theremoving of the first volume of the first liquid culture medium and theadding of the second volume of the second liquid culture medium in oneor more of the first time period, the second time period, and the thirdtime period is performed simultaneously. In some embodiments of any ofthese methods, the removing of the first volume of the first liquidculture medium and the adding of the second volume of the second liquidculture medium in one or more of the first time period, the second timeperiod, and the third time period is performed continuously. In someembodiments of any of these methods, the removing of the first volume ofthe first liquid culture medium and the adding of the second volume ofthe second liquid culture medium in one of more of the first timeperiod, the second time period, and the third time period is performedperiodically. In some embodiments of any of these methods, the shakeflask is gas-permeable and has a volume of between about 20 mL to about1 L. In some embodiments of any of these methods, the volume of thefirst liquid culture medium is about 40 mL to about 80 mL. In someembodiments of any of these methods, the first liquid culture medium andsecond liquid culture medium used in the first time period isserum-containing liquid culture medium or an animal-derivedcomponent-containing liquid culture medium, and the first liquid culturemedium and second liquid culture medium used in the second time periodand the third time period is a serum-free liquid culture medium, ananimal-derived component free liquid culture medium, or a protein-freemedium. In some embodiments of any of these methods, the agitation isceased for at least 30 seconds prior to removing the first volume of thefirst liquid culture medium, from the shake flask during one or more ofthe first time period, the second time period, and the third timeperiod. In some embodiments of any of these methods, the plurality ofmicrocarriers has a mean diameter of between about 200 μm to about 800μm. In some embodiments of any of these methods, the plurality ofmicrocarrier contains one or more pores. In some embodiments of any ofthese methods, the one or more pores has a mean diameter of about 25 μmto about 35 μm. In some embodiments of any of these methods, the firstvolume of the liquid culture medium removed during the third period oftime contains a substantial number of microcarriers. In some embodimentsof any of these methods, the first volume of the liquid culture mediumremoved during the third period of time is substantially free ofmicrocarriers. In some embodiments of any of these methods, the firstvolume of the first liquid culture medium removed and the second volumeof the second liquid culture medium added in one or more of the firsttime period, the second time period, and the third time period is about70% of the volume of the first liquid culture medium. In someembodiments of any of these methods, the shake flask is incubated in oneor more of (b), (c), and (d) at a reactor angle of about 25 degrees toabout 90 degrees from horizontal, or at an angle that is about 45degrees relative to the benchtop or the horizon.

Also provided are methods for testing a manufacturing process for makinga recombinant protein. These methods include: providing a shake flaskcontaining a mammalian cell containing a nucleic acid encoding arecombinant protein disposed in a first liquid culture medium, where thefirst liquid culture medium occupies about 20% to about 30% of thevolume of the shake flask and contains a plurality of microcarriers at aconcentration of about 1.0 g/L to about 15.0 g/L; incubating the shakeflask for a period of time at about 32° C. to about 39° C. and with arotary agitation of about 85 revolutions per minute (RPM) to about 125RPM; after about the first 48 to 96 hours of the period of time,continuously or periodically removing a first volume of the first liquidculture medium and adding to the first liquid culture medium a secondvolume of a second liquid culture medium, where the first and secondvolumes are about equal; detecting the recombinant protein in the cellor in the first and/or second culture medium; and comparing the amountof recombinant protein present in the cell or in the first and/or secondculture medium to a reference level of recombinant protein. In someembodiments of any of these methods, the first volume of the firstliquid culture medium is substantially free of mammalian cells. In someembodiments of any of these methods, the reference level of recombinantprotein is a level of recombinant protein produced using a differentculturing method. In some embodiments of any of these methods, thedifferent culturing method utilizes a different first or second liquidculture medium, a different mammalian cell, a different temperature, adifferent level of agitation, a different shake flask, or a differentmicrocarrier. In some embodiments of any of these methods, the differentculturing method utilizes different raw materials, anti-clumping agents,or chemically-defined liquid culture media. In some embodiments of anyof these methods, the method is used to perform high throughput cellculture experiments to perform a design-of-experiment (DOE) or aquality-by-design (QBD) study. In some embodiments of any of thesemethods, the first liquid culture medium occupies about 25% to about 30%of the volume of the shake flask. In some embodiments of any of thesemethods, the shake flask is gas-permeable and has a volume of betweenabout 20 mL to about 1 L. In some embodiments of any of these methods,the mammalian cell is suspended in about 40 mL to about 80 mL of thefirst liquid culture medium. In some embodiments of any of the methodsdescribed herein, the mammalian cell is a Chinese hamster ovary (CHO)cell. In some embodiments of any of these methods, the recombinantprotein is a secreted immunoglobulin, a secreted enzyme, a secretedgrowth factor, a secreted protein fragment, or a secreted engineeredprotein, and where the recombinant protein is recovered from the firstor second culture medium. In some embodiments of any of these methods,the recombinant protein is recovered from the mammalian cell. In someembodiments of any of these methods, the recombinant protein is animmunoglobulin, an enzyme, a growth factor, a protein fragment, or anengineered protein. In some embodiments of any of these methods, theremoving of the first volume of the first liquid culture medium and theadding of the second volume of the second liquid culture medium isperformed simultaneously. In some embodiments of any of these methods,the removing of the first volume of the first liquid culture medium andthe adding of the second volume of the second liquid culture medium isperformed continuously. In some embodiments of any of these methods, theremoving of the first volume of the first liquid culture medium and theadding of the second volume of the second liquid culture medium isperformed periodically. In some embodiments of any of these methods, thefirst volume of the first liquid culture medium removed and the secondvolume of the second liquid culture medium added are increased overtime. In some embodiments of any of these methods, the first liquidculture medium and/or second liquid culture medium is selected from thegroup of: a chemically-defined liquid culture medium, a serum-freeliquid culture medium, a serum-containing liquid culture medium, ananimal-derived component free liquid culture medium, and a protein-freemedium. In some embodiments of any of these methods, the shake flask isincubated at a reactor angle of about 25 degrees to about 90 degreesfrom horizontal, or at an angle that is about 45 degrees relative to thebenchtop or the horizon.

Also provided are methods of testing the efficacy of a first or secondliquid culture medium, a raw ingredient or supplement present in a firstor second liquid culture medium, or a source of a mammalian cell for usein a method of producing a recombinant protein. These methods include:providing a shake flask containing a mammalian cell disposed in a firstliquid culture medium, where the first liquid culture medium occupiesabout 20% to about 30% of the volume of the shake flask and contains aplurality of microcarriers at a concentration of about 1.0 g/L to about15.0 g/L; incubating the shake flask for a period of time at about 32°C. to about 39° C. and with a rotary agitation of about 85 revolutionsper minute (RPM) to about 125 RPM; and after about the first 48 to 96hours of the period of time, continuously or periodically removing afirst volume of the first liquid culture medium and adding to the firstliquid culture medium a second volume of a second liquid culture medium,where the first and second volumes are about equal; detecting therecombinant protein in the cell or in the first and/or second culturemedium; comparing the amount of recombinant protein present in the cellor in the first and/or second culture medium to a reference level ofrecombinant protein produced by a different method that uses one or moreof a different first or second liquid culture medium, a different rawingredient or supplement present in the first or second liquid culturemedium, or a different source of a mammalian cell; and identifying thefirst or second liquid culture medium, the raw ingredient or supplementpresent in the first or second liquid culture medium, or the source ofthe mammalian cell that is associated with an increased amount ofrecombinant protein as compared to the reference level as beingefficacious for use in a method of producing a recombinant protein. Insome embodiments of any of these methods, the shake flask is incubatedat a reactor angle of about 25 degrees to about 90 degrees fromhorizontal, or at an angle that is about 45 degrees relative to thebenchtop or the horizon.

Also provided are methods of optimizing a manufacturing process ofproducing a recombinant protein. These methods include: providing ashake flask containing a mammalian cell disposed in a first liquidculture medium, where the first liquid culture medium occupies about 20%to about 30% of the volume of the shake flask and contains a pluralityof microcarriers at a concentration of about 1.0 g/L to about 15.0 g/L;incubating the shake flask for a period of time at about 32° C. to about39° C. and with a rotary agitation of about 85 revolutions per minute(RPM) to about 125 RPM; and after about the first 48 to 96 hours of theperiod of time, continuously or periodically removing a first volume ofthe first liquid culture medium and adding to the first liquid culturemedium a second volume of a second liquid culture medium, where thefirst and second volumes are about equal; detecting the recombinantprotein in the cell or in the first and/or second culture medium;comparing the amount of recombinant protein present in the cell or inthe first and/or second culture medium to a reference level ofrecombinant protein produced by a different method; and identifying andremoving or altering in a manufacturing process any culture componentsor parameters that are associated with a decrease in the amount ofrecombinant protein produced as compared to the reference level, oridentifying and adding to a manufacturing process any culture componentsor parameters that are associated with an increase in the amount ofrecombinant protein produced as compared to the reference level. In someembodiments of any of these methods, the shake flask is incubated at areactor angle of about 25 degrees to about 90 degrees from horizontal,or at an angle that is about 45 degrees relative to the benchtop or thehorizon.

Also provided are methods of testing for the presence of a contaminantin a first or second liquid culture medium, a raw material used togenerate a first or second liquid culture medium, or a source of amammalian cell. These methods include: providing a shake flaskcontaining a mammalian cell disposed in a first liquid culture medium,where the first liquid culture medium occupies about 20% to about 30% ofthe volume of the shake flask and contains a plurality of microcarriersat a concentration of about 1.0 g/L to about 15.0 g/L; incubating theshake flask for a period of time at about 32° C. to about 39° C. andwith a rotary agitation of about 85 revolutions per minute (RPM) toabout 125 RPM; and after about the first 48 to 96 hours of the period oftime, continuously or periodically removing a first volume of the firstliquid culture medium and adding to the first liquid culture medium asecond volume of a second liquid culture medium, where the first andsecond volumes are about equal; detecting the recombinant protein in thecell or in the first and/or second culture medium; comparing the amountof recombinant protein present in the cell or in the first and/or secondculture medium to a reference level of recombinant protein produced by adifferent method that uses one or more of a different first or secondliquid culture medium, a different raw material to generate the first orsecond liquid culture medium, or a different source of the mammaliancell; and identifying the first or second liquid culture medium, the rawmaterial used to generate the first or second liquid culture medium, orthe source of a mammalian cell as containing a contaminant when thelevel of recombinant protein produced is less than the reference level.In some embodiments of any of these methods, the contaminant is abiological contaminant. In some embodiments of any of these methods, thebiological contaminant is selected from the group of: mycobacterium, afungus, a bacterium, a virus, and an undesired mammalian cell. In someembodiments of any of these methods, the shake flask is incubated at areactor angle of about 25 degrees to about 90 degrees from horizontal,or at an angle that is about 45 degrees relative to the benchtop or thehorizon.

As used herein, the word “a” or “plurality” before a noun represents oneor more of the particular noun. For example, the phrase “a mammaliancell” represents “one or more mammalian cells,” and the phrase“plurality of microcarriers” means “one or more microcarriers.”

The term “mammalian cell” means any cell from or derived from any mammal(e.g., a human, a hamster, a mouse, a green monkey, a rat, a pig, a cow,or a rabbit. In some embodiments, the mammalian cell can be, e.g., animmortalized cell, a differentiated cell, or an undifferentiated cell.

The term “target cell density” means a specific concentration of cellsper volume of culture medium for producing a recombinant protein inculture. Target cell density can vary depending upon the specificmammalian cell cultured. For example, the target cell density can beabout 1.0×10⁶ cells/mL to about 50×10⁶ cells/mL (e.g., between about2.0×10⁶ cells/mL to about 3.0×10⁶ cells/mL).

The term “substantially free” means a composition (e.g., a liquidculture medium) that is at least or about 90% free (e.g., at least orabout 95%, 96%, 97%, 98%, or at least or about 99% free, or about 100%free) of a specific substance (e.g., a mammalian cell or microcarriers).

The term “culturing” or “cell culturing” means the maintenance or growthof a mammalian cell in a liquid culture medium under a controlled set ofphysical conditions.

The term “shake flask” is meant a vessel (e.g., a sterile vessel) thatcan hold a volume of liquid culture medium that has at least one gaspermeable surface (e.g., an end that has at a gas-permeable element,e.g., a membrane, which may also act as a sterile barrier) and/or atleast one vent cap, and at least a portion of its shape is approximatelyfrustoconical. For example, a shake flask can be a cell culture flask,such as a T-flask, an Erlenmeyer flask, or any art-recognized modifiedversion thereof.

The term “liquid culture medium” means a fluid that contains sufficientnutrients to allow a mammalian cell to grow in the medium in vitro. Forexample, a liquid culture medium can contain one or more of: amino acids(e.g., 20 amino acids), a purine (e.g., hypoxanthine), a pyrimidine(e.g., thymidine), choline, inositol, thiamine, folic acid, biotin,calcium, niacinamide, pyridoxine, riboflavin, thymidine, cyanocobalamin,pyruvate, lipoic acid, magnesium, glucose, sodium, potassium, iron,copper, zinc, selenium, and other necessary trace metals, and sodiumbicarbonate. A liquid culture medium may contain serum from a mammal. Insome instances, a liquid culture medium does not contain serum oranother extract from a mammal (a defined liquid culture medium). Aliquid culture medium may contain trace metals, a mammalian growthhormone, and/or a mammalian growth factor. Non-limiting examples ofliquid culture medium are described herein and additional examples areknown in the art and are commercially available.

The phrase “substantially different type of liquid culture medium” meansa liquid culture medium that contains a substantially different nutrientprofile from another liquid culture medium. For example, a liquidculture medium that contains one or more of a mammalian serum, mammalianprotein, or a mammalian protein fraction or extract (e.g., aserum-containing liquid culture medium) is a substantially differenttype of liquid culture medium than one that does not contain any of amammalian serum, mammalian protein, or a mammalian protein fraction orextract (e.g., an animal-derived component free liquid culture medium, aserum-free liquid culture medium, a chemically-defined liquid culturemedium, and a protein-free liquid culture medium).

The phrase “substantially the same type of liquid culture medium” meansa liquid culture medium that contains about the same nutrient profile ascompared to another liquid culture medium. For example, if liquidculture medium A and liquid culture medium B both contain one or more ofa mammalian serum, mammalian protein, and a mammalian protein fractionor extract (e.g., a serum-containing liquid culture medium), there aresubstantially the same. In another example, if liquid culture medium Aand liquid culture medium B both do not contain any of a mammalianserum, mammalian protein, and a mammalian protein fraction or extract(e.g., an animal-derived component free liquid culture medium, aserum-free liquid culture medium, a chemically-defined liquid culturemedium, and a protein-free liquid culture medium), they aresubstantially the same.

The term “microcarrier” means a particle (e.g., an organic polymer) thathas a size of between 20 μm to about 1000 μm that contains a surfacethat is permissive or promotes attachment of a mammalian cell (e.g., anyof the mammalian cells described herein or known in the art). Amicrocarrier can contain one or more pores (e.g., pores with an averagediameter of about 10 μm to about 100 μm). Non-limiting examples ofmicrocarriers are described herein. Additional examples of microcarriersare known in the art. A microcarrier can contain, e.g., a polymer (e.g.,cellulose, polyethylene glycol, or poly-(lactic-co-glycolic acid)).

The term “animal-derived component free liquid culture medium” means aliquid culture medium that does not contain any components (e.g.,proteins or serum) derived from an animal.

The term “serum-free liquid culture medium” means a liquid culturemedium that does not contain animal serum.

The term “serum-containing liquid culture medium” means a liquid culturemedium that contains animal serum.

The term “chemically-defined liquid culture medium” means a liquidculture medium in which substantially all of the chemical components areknown. For example, a chemically-defined liquid culture medium does notcontain fetal bovine serum, bovine serum albumin, or human serumalbumin, as these preparations typically contain a complex mix ofalbumins and lipids.

The term “protein-free liquid culture medium” means a liquid culturemedium that does not contain any protein (e.g., any detectable protein).

“Rotary agitation” is a term well-known in the art and refers to themovement of a shake flask in a generally circular fashion, e.g.,clock-wise or counter-clockwise, in order to, e.g., increase thedissolved O₂ concentration in a liquid culture medium contained therein.Agitation can be performed using any art-known method, e.g., aninstrument that moves the shake flask in a circular or ellipsoidalmotion, such as a rotary shaker. Exemplary devices that can be used toperform rotary agitation are described herein. Additional examples ofsuch devices are also known in the art and are commercially available.

The term “immunoglobulin” means a polypeptide containing an amino acidsequence of at least 15 amino acids (e.g., at least 20, 30, 40, 50, 60,70, 80, 90, or 100 amino acids) of an immunoglobulin protein (e.g., avariable domain sequence, a framework sequence, or a constant domainsequence). The immunoglobulin may, for example, include at least 15amino acids of a light chain immunoglobulin, e.g., at least 15 aminoacids of a heavy chain immunoglobulin. The immunoglobulin may be anisolated antibody (e.g., an IgG, IgE, IgD, IgA, or IgM). Theimmunoglobulin may be a subclass of IgG (e.g., IgG1, IgG2, IgG3, orIgG4). The immunoglobulin may be an antibody fragment, e.g., a Fabfragment, a F(ab′)₂ fragment, or an a scFv fragment. The immunoglobulinmay also be a bi-specific antibody or a tri-specific antibody, or adimer, trimer, or multimer antibody, or a diabody, an Affibody®, or aNanobody®. The immunoglobulin can also be an engineered proteincontaining at least one immunoglobulin domain (e.g., a fusion protein).Non-limiting examples of immunoglobulins are described herein andadditional examples of immunoglobulins are known in the art.

The term “protein fragment” or “polypeptide fragment” means a portion ofa polypeptide sequence that is at least or about 4 amino acids, at leastor about 5 amino acids, at least or about 6 amino acids, at least orabout 7 amino acids, at least or about 8 amino acids, at least or about9 amino acids, at least or about 10 amino acids, at least or about 11amino acids, at least or about 12 amino acids, at least or about 13amino acids, at least or about 14 amino acids, at least or about 15amino acids, at least or about 16 amino acids, at least or about 17amino acids, at least or about 18 amino acids, at least or about 19amino acids, or at least or about 20 amino acids in length, or more than20 amino acids in length. A recombinant protein fragment can be producedusing any of the methods described herein.

The term “engineered protein” means a polypeptide that is not naturallyencoded by an endogenous nucleic acid present within an organism (e.g.,a mammal). Examples of engineered proteins include enzymes (e.g., withone or more amino acid substitutions, deletions, insertions, oradditions that result in an increase in stability and/or catalyticactivity of the engineered enzyme), fusion proteins, antibodies (e.g.,divalent antibodies, trivalent antibodies, or a diabody), andantigen-binding proteins that contain at least one recombinantscaffolding sequence.

The term “recover” or “recovering” in certain contexts means at leastpartially purifying or isolating (e.g., at least or about 5%, e.g., atleast or about 10%, 15%, 20%, 25%, 30%, 40%, 45%, 50%, 55%, 60%, 65%,70%, 75%, 80%, 85%, 90%, or at least or about 95% pure by weight) arecombinant protein from one or more other components present in thecell culture medium (e.g., mammalian cells or culture medium proteins)or one or more other components (e.g., DNA, RNA, or other proteins)present in a mammalian cell lysate. Non-limiting methods for recoveringa protein from a liquid culture medium or from a mammalian cell lysateare described herein and others are known in the art.

The term “secreted protein” or “secreted recombinant protein” means aprotein or a recombinant protein that originally contained at least onesecretion signal sequence when it is translated within a mammalian cell,and through, at least in part, enzymatic cleavage of the secretionsignal sequence in the mammalian cell, is released into theextracellular space (e.g., a liquid culture medium).

The phrase “gradient perfusion” is art-known and refers to theincremental change (e.g., increase or decrease) in the volume of culturemedium removed and added to an initial culture over incremental periods(e.g., an about 24-hour period, a period of between about 1 minute andabout 24-hours, or a period of greater than 24 hours) during theculturing period (e.g., the culture medium re-feed rate on a dailybasis). The fraction of media removed and replaced each day can varydepending on the particular cells being cultured, the initial seedingdensity, and the cell density at a particular time.

The term “feed-batch culture” means the incremental or continuousaddition of a second liquid culture medium to an initial cell culturewithout substantial or significant removal of the first liquid culturemedium from the cell culture. In some instances, the second liquidculture medium is the same as the first liquid culture medium. In otherinstances, the second liquid culture medium is a concentrated form ofthe first liquid culture medium and/or is added as a dry powder.

The term “reactor angle” refers to the angle of deviation from thehorizontal position that the shake flask containing a mammalian cell isplaced during the culturing methods described herein. For example, whenthe shake flask containing a mammalian cell is standing verticalrelative to the lab bench or ground, the reactor angle is 90°, and whenthe shake flask containing a mammalian cell is placed horizontalrelative to the lab bench or ground, the reactor angle is 0°. In anotherexample, when a shake flask containing a mammalian cell is placedequidistant between the vertical and horizontal positions (relative tothe lab bench or ground), the reactor angle is 45°.

“Specific productivity rate” or “SPR” as used herein refers to the massor enzymatic activity of a recombinant protein produced per mammaliancell per day. The SPR for a recombinant antibody is usually measured asmass/cell/day. The SPR for a recombinant enzyme is usually measured asunits/cell/day or (units/mass)/cell/day.

“Volume productivity rate” or “VPR” as used herein refers to the mass orenzymatic activity of recombinant protein produced per volume of culture(e.g., per L of bioreactor, vessel, or tube volume) per day. The VPR fora recombinant antibody is usually measured as mass/L/day. The VPR for arecombinant enzyme is usually measured as units/L/day or mass/L/day.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Methods and materials aredescribed herein for use in the present invention; other, suitablemethods and materials known in the art can also be used. The materials,methods, and examples are illustrative only and not intended to belimiting. All publications, patent applications, patents, sequences,database entries, and other references mentioned herein are incorporatedby reference in their entirety. In case of conflict, the presentspecification, including definitions, will control.

Other features and advantages of the invention will be apparent from thefollowing detailed description and figures, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing an exemplary rack that can be used toposition the shake flask at an angle of about 45 degrees relative to thebenchtop or the horizon, that can be used in any of the methodsdescribed herein.

FIG. 2 is a graph showing the average viable cell concentration overtime in recombinant human alpha-galactosidase shake flask microcarrierbatch re-feed cell culture process runs (n=5) and 2000-L bioreactor cellculture process runs (n=9). The shaded areas represent the standarddeviation of the data.

FIG. 3 is a graph showing the average percentage of viable cells overtime in recombinant human alpha-galactosidase shake flask microcarrierbatch re-feed cell culture process runs (n=5). The shaded arearepresents the standard deviation of the data.

FIG. 4 is a graph showing the average concentration of suspended cells(the concentration of cells not adhering to the microcarriers in theliquid culture medium) over time in recombinant humanalpha-galactosidase shake flask microcarrier batch re-feed cell cultureprocess runs (n=5). The shaded area represents the standard deviation ofthe data.

FIG. 5 is a graph of the average volumetric productivity over time inrecombinant human alpha-galactosidase shake flask microcarrier batchre-feed cell culture process runs (n=5) and 2000-L bioreactor cellculture process runs (n=9). The shaded areas represent the standarddeviation of the data.

FIG. 6 is a graph of the cumulative volumetric productivity (units/L)over time in recombinant human alpha-galactosidase shake flaskmicrocarrier batch-refeed cell culture process runs (n=3) and inrecombinant human alpha-galactosidase 2000-L bioreactor culture processruns (n=3).

FIG. 7 is a graph of the viable cell concentration over time for shakeflask microcarrier batch re-feed cell culture process runs containingdifferent: types of liquid culture medium (liquid culture medium A orB), concentrations of microcarrier (a concentration of microcarriers of1.0 g/L or 1.5 g/L), and/or different frequencies of rotation (85 RPM or125 RPM).

FIG. 8 is a schematic diagram of the growth phase and harvest phasesatellite shake flask culture study.

FIG. 9 is a graph of the viable cell concentration in the growth phasesatellite shake flask cultures and the 40-L bioreactor cultures overtime. The error bars represent +/−1 standard deviation of the data(n=2). “1” represents the time point when the frequency of agitation wasincreased from 85 RPM to 95 RPM. The growth phase satellite shake flaskculture data was shifted by −1 day in order to more accurately comparethe data to the 40-L bioreactor culture data.

FIG. 10 is a graph of the percentage of viable cells in the growth phasesatellite shake flask cultures and the 40-L bioreactor cultures overtime. The error bars represent +/−1 standard deviation of the data(n=2). “1” represents the time point when the frequency of agitation wasincreased from 85 RPM to 95 RPM. The growth phase satellite shake flaskculture data was shifted by −1 day in order to more accurately comparethe data to the 40-L bioreactor culture data.

FIG. 11 is a graph of the suspended cell concentration in the growthphase satellite shake flask cultures and the 40-L bioreactor culturesover time. The error bars represent +/−1 standard deviation of the data(n=2). “1” represents the time point when the frequency of agitation wasincreased from 85 RPM to 95 RPM. The growth phase satellite shake flaskculture data was shifted by −1 day in order to more accurately comparethe data to the 40-L bioreactor culture data.

FIG. 12 is a graph of the titer (units/L) of recombinant humanalpha-galactosidase in the growth phase satellite shake flask culturesand the 40-L bioreactor cultures over time. The error bars represent+/−1 standard deviation of the data (n=2). The growth phase satelliteshake flask culture data was shifted by −1 day in order to moreaccurately compare the data to the 40-L bioreactor culture data.

FIG. 13 is a graph of the specific productivity of recombinant humanalpha-galactosidase (units per 1×10⁶ cells) for the growth phasesatellite shake flask cultures and the 40-L bioreactor cultures overtime. The error bars represent +/−1 standard deviation of the data(n=2). The growth phase satellite shake flask culture data was shiftedby −1 day in order to more accurately compare the data to the 40-Lbioreactor culture data.

FIG. 14 is a graph of the yield of lactate from glucose (moles oflactate/moles of glucose) for the growth phase satellite shake flaskcultures and the 40-L bioreactor cultures over time. The error barsrepresent +/−1 standard deviation of the data (n=2). The growth phasesatellite shake flask culture data was shifted by −1 day in order tomore accurately compare the data to the 40-L bioreactor culture data.

FIG. 15 is a graph of the viable cell concentration of the harvest phasesatellite shake flask cultures and the 40-L bioreactor cultures overtime. The average data are shown (40-L, n=3; 68 mL at 95 RPM, n=3; 60 mLat 95 RPM, n=2; and 60 mL at 110 RPM, n=2), with the error barsrepresenting +/−1 standard deviation of the data.

FIG. 16 is a graph of the percentage of viable cells in the harvestphase satellite shake flask cultures and the 40-L bioreactor culturesover time. The average data are shown (40-L, n=3; 68 mL at 95 RPM, n=3;60 mL at 95 RPM, n=2; and 60 mL at 110 RPM, n=2), with the error barsrepresenting +/−1 standard deviation of the data.

FIG. 17 is a graph of the suspended cell concentration in the harvestphase satellite shake flask cultures and the 40-L bioreactor culturesover time. The average data are shown (40 L, n=3; 68 mL at 95 RPM, n=3;60 mL at 95 RPM, n=2; and 60 mL at 110 RPM, n=2), with the error barsrepresenting +/−1 standard deviation of the data.

FIG. 18 is a graph of the titer of recombinant human alpha-galactosidase(units/L) in the harvest phase satellite shake flask cultures and the40-L bioreactor cultures over time. The average data are shown (40 L,n=3; 68 mL at 95 RPM, n=3; 60 mL at 95 RPM, n=2; and 60 mL at 110 RPM,n=2), with the error bars representing +/−1 standard deviation of thedata.

FIG. 19 is a graph of the specific productivity of recombinant humanalpha-galactosidase (units per 1×10⁶ cells) for the harvest phasesatellite shake flask cultures and the 40-L bioreactor cultures overtime. The average data are shown (40 L, n=3; 68 mL at 95 RPM, n=3; 60 mLat 95 RPM, n=2; and 60 mL at 110 RPM, n=2), with the error barsrepresenting +/−1 standard deviation of the data.

FIG. 20 is a graph of the yield of recombinant human alpha-galactosidaseper gram of glucose (units/g) for the harvest phase satellite shakeflask cultures and the 40-L bioreactor cultures over time. The averagedata are shown (40 L, n=3; 68 mL at 95 RPM, n=3; 60 ml, at 95 RPM, n=2;and 60 mL at 110 RPM, n=2), with the error bars representing +/−1standard deviation of the data.

FIG. 21 is a graph of the yield of lactate from glucose (moles oflactate/moles of glucose) for the harvest phase satellite shake flaskcultures and the 40-L bioreactor cultures over time. The average dataare shown (40 L, n=3; 68 mL at 95 RPM, n=3; 60 mL at 95 RPM, n=2; and 60mL at 110 RPM, n=2), with the error bars representing +/−1 standarddeviation of the data.

FIG. 22 is a graph of the percentage of the apoptotic cells present inthe harvest phase satellite shake flask cultures and the 40-L bioreactorcultures over time. The average data are shown (40 L, n=3; 68 mL at 95RPM, n=3; 60 mL at 95 RPM, n=2; and 60 mL at 110 RPM, n=2), with theerror bars representing +/−1 standard deviation of the data.

FIG. 23 is a graph of the percentage of non-apoptotic cells present inthe harvest phase satellite shake flask cultures and the 40 L bioreactorcultures over time. The average data are shown (40 L, n=3; 68 mL at 95RPM, n=3; 60 mL at 95 RPM, n=2; and 60 mL at 110 RPM, n=2), with theerror bars representing +/−1 standard deviation of the data.

FIG. 24 is a schematic diagram showing the design of the harvest phasesatellite shake flask CD-hydrolysate study.

FIG. 25 is a graph of the viable cell concentration in each harvestphase satellite shake flask culture and each 40-L bioreactor cultureover time.

FIG. 26 is a graph of the percentage of viable cells in each harvestphase satellite shake flask culture and each 40-L bioreactor cultureover time.

FIG. 27 is a graph of the suspended cell concentration over time in eachharvest phase satellite shake flask culture and each 40-L bioreactorculture over time.

FIG. 28 is a graph of the titer (units/L) of recombinant humanalph-galactosidase present in each harvest phase satellite shake flaskculture and each 40-L bioreactor culture over time.

FIG. 29 is a graph of the specific productivity rate (SPR) ofrecombinant human alpha-galactosidase (units/[1×10⁹ cells·day]) for eachharvest phase satellite shake flask culture and each 40-L bioreactorculture over time.

DETAILED DESCRIPTION

Provided herein are improved methods of culturing a mammalian cell in ashake flask using a plurality of microcarriers and batch re-feedperfusion. The culturing methods described herein can achieve highmammalian cell concentration levels, thereby improving the overallefficiency of a culturing process and providing high yields of desirablecellular products, such as recombinant proteins. For example, themethods can provide a viable mammalian cell concentration (e.g., in thefirst and/or second liquid culture medium, or the first and/or secondliquid culture medium in one or more of the first, second, and thirdtime periods) of greater than 2×10⁶ cells per mL, greater than 3×10⁶cells/mL, greater than 4×10⁶ cells/mL, greater than 5×10⁶ cells/mL,greater than 6×10⁶ cells/mL, greater than 7×10⁶ cells/mL, greater than8×10⁶ cells/mL, greater than 9×10⁶ cells/mL, greater than 10×10⁶cells/mL, greater than 12×10⁶ cells/mL, greater than 14×10⁶ cells/mL,greater than 16×10⁶ cells/mL, greater than 18×10⁶ cells/mL, greater than20×10⁶ cells/mL, greater than 25×10⁶ cells/mL, greater than 30×10⁶cells/mL, greater than 35×10⁶ cells/mL, greater than 40×10⁶ cells/mL,greater than 45×10⁶ cells/mL, or greater than 50×10⁶ cells/mL. Forexample, the culturing method can result in a viable mammalian cellconcentration of between 1×10⁶ cells/mL and 3×10⁶ cells/mL, between3×10⁶ cells/mL and 5×10⁶ cells/mL, between 5×10⁶ cells/mL and 7×10⁶cells/mL, between 7×10⁶ cells/mL and 9×10⁶ cells/mL, between 9×10×10⁶cells/mL and 11×10⁶ cells/mL, between 10×10⁶ cells/mL and 12×10⁶cells/mL, between 11×10⁶ cells/mL and 13×10⁶ cells/mL, between 12×10⁶cells/mL and 14×10⁶ cells/mL, between 14×10⁶ cells/mL and 16×10⁶cells/mL, between 16×10⁶ cells/mL and 18×10⁶ cells/mL, between 18×10⁶cells/mL and 20×10⁶ cells/mL, between 20×10⁶ cells/mL and 25×10⁶cells/mL, between 25×10⁶ cells/mL and 30×10⁶ cells/mL, between 30×10⁶cells/mL and 35×10⁶ cells/mL, between 35×10⁶ cells/mL and 40×10⁶cells/mL, between 40×10⁶ cells/mL and 45×10⁶ cells/mL, between 45×10⁶cells/mL and 50×10⁶ cells/mL, or greater than 50×10⁶ cells/mL. In someinstances, the methods described herein result in an increase in thebiological activity of a recombinant protein (e.g., as compared to thebiological activity of a recombinant protein produced by a differentmethod).

A variety of different methods to determine the cell density or viablecell density can be used, and are well-known in the art. For example, asample of the cell culture containing microcarriers can be treated torelease the cells from the surface of the microcarriers, and thereleased cells can optionally be diluted in physiological buffer, andthe cell suspension (e.g., diluted cell suspension) placed in ahemocytometer and counted using light microscopy. In another method, theviable cell density can be determined using a similar method, butincluding in the physiological buffer a dye that is selectively taken upby non-viable cells (e.g., trypan blue, such as Vi-CELL method fromBeckman Coulter (see Beckman Coulter website)). In yet another example,the cell density or viable cell density can be determined usingfluorescence-assisted flow cytometry (e.g., GUAVA from Merck Millipore(see Millipore website), and other cell counting methods.

In some instances, the culturing method results in a significantlyimproved specific productivity rate. For example, the specificproductivity rate achieved by the methods provided herein can be atleast 2-fold, 3-fold, 4-fold, 5-fold, 6-fold, 7-fold, 8-fold, 9-fold,10-fold, 20-fold, 30-fold, 40-fold, 50-fold, 60-fold, 70-fold, 80-fold,90-fold, 100-fold, 110-fold, 120-fold, 130-fold, 140-fold, 150-fold,160-fold, 170-fold, 180-fold, 190-fold, or 200-fold greater than thespecific productivity rate achieved using an art-known culturing method(e.g., a different shake flask culture method). The volume productivityachieved by the present methods can be at least 300 units/L/day, atleast 400 units/L/day, at least 500 units/L/day, at least 600units/L/day, at least about 800 units/L/day, at least about 1,000units/L/day, at least about 1,200 units/L/day, at least about 1,400units/L/day, at least about 1,600 units/L/day, at least about 1,800units/L/day, at least about 2,000 units/L/day, at least about 2,200units/L/day, at least about 3,000 units/L/day, at least 4,000units/L/day, at least 5,000 units/L/day, at least 6,000 units/L/day, atleast 7,000 units/L/day, at least 8,000 units/L/day, at least 9,000units/L/day, at least 10,000 units/L/day, or higher than 10,000units/L/day (e.g., in the first and/or second liquid culture medium, orthe first and/or second liquid culture medium used in one or more of thefirst, second, and third time period). In some embodiments, theproductivity achieved by the present methods can be at least 0.2 g/L, atleast 0.5 g/L, at least 0.75 g/L, at least 1.0 g/L, at least 1.25 g/L,at least 1.5 g/L, at least 1.75 g/L, at least 2.0 g/L, at least 2.5 g/L,at least 3.0 g/L, at least 3.5 g/L, at least 4.0 g/L, at least 4.5 g/L,or at least 5.0 g/L (e.g., in the first and/or second liquid culturemedium, or the first and/or second liquid culture medium used in thefirst, second, and third time period).

The biological activity of a recombinant protein can be assessed using avariety of methods known in the art, and will depend on the activity ofthe specific recombinant protein. For example, the biological activityof a recombinant protein that is an immunoglobulin (e.g., an antibody oran antibody fragment) can be determined by measuring the affinity of theantibody to bind to its specific epitope (e.g., using Biocore orcompetitive enzyme-linked immunosorbent assays). The recombinant proteinmay be an enzyme (e.g., a recombinant galactosidase, e.g., a recombinantalpha-galactosidase) and the biological activity may be determined bymeasuring the enzyme's activity (e.g., determining the catalytic rateconstant of the enzyme by measuring a decrease in the concentration of adetectable substrate or an increase in the concentration of a detectableproduct (e.g., using spectrophotometry or light emission). For example,the biological activity of a recombinant galactosidase can be detectedby measuring a decrease in the level of globotriasylceramide (GL-3) orgalabiosylceramide, or an increase in the level of ceramide dihexosideor galactose.

Methods of Culturing a Mammalian Cell

In a method that is exemplary of those described herein, a shake flaskis provided. A first liquid culture medium is added to the shake flasksuch that the medium occupies, about 10% to about 40%, e.g., about 20%to about 30% (e.g., about 20% to about 22%, about 22% to about 24%,about 24% to about 26%, about 26% to about 28%, about 28% to about 30%,about 20% to about 25%, or about 25% to about 30%) of the volume of theshake flask. At least one mammalian cell and a plurality ofmicrocarriers (a final concentration in the shake flask of about 1.0 g/Lto about 15.0 g/L, e.g., a final concentration in the shake flask ofbetween about 1.0 g/L to about 2.5 g/L, about 1.0 g/L to about 2.0 g/L,about 1.0 g/L to about 1.75 g/L, about 1.0 g/L to about 1.5 g/L, about1.0 g/L to about 1.25 g/L, about 2.5 g/L to 5.0 g/L, about 5.0 g/L toabout 7.5 g/L, about 7.5 g/L to about 10.0 g/L, about 10.0 g/L to about12.5 g/L, about 12.5 g/L to about 15.0 g/L, about 1.0 g/L to about 5.0g/L, about 5.0 g/L to about 10.0 g/L, about 10.0 g/L to about 15.0 g/L,about 2.5 g/L to about 3.5 g/L, about 3.0 g/L to about 4.0 g/L, about4.0 g/L to about 5.0 g/L, about 5.0 g/L to about 6.0 g/L, about 6.0 g/Lto about 7.0 g/L, about 7.0 g/L to about 8.0 g/L, about 8.0 g/L to about9.0 g/L, about 9.0 g/L to about 10.0 g/L, about 10.0 g/L to about 11.0g/L, about 11.0 g/L to about 12.0 g/L, about 12.0 g/L to about 13.0 g/L,about 13.0 g/L to about 14.0 g/L, or about 14.0 g/L to about 15.0 g/L)is added to the first liquid culture medium, i.e., either before themedium is added to the shake flask or afterward. As one skilled in theart can appreciate, the steps of the addition of the liquid culturemedium, a mammalian cell, and the liquid culture medium to the shakeflask can occur in any order. The shake flask is incubated for a periodof time at about 32° C. to about 39° C. (e.g., 32° C. to 34° C., 32° C.to 37° C., 34° C. to 37° C., 37° C. to 39° C.) and agitated, e.g., on arotary shaking device, at about 85 RPM to about 125 RPM (e.g., about 85RPM to about 120 RPM, about 85 RPM to about 110 RPM, about 85 RPM toabout 100 RPM, about 85 RPM to about 95 RPM, about 85 RPM to about 105RPM, about 90 RPM to about 110 RPM, about 95 RPM to about 115 RPM, about100 RPM to about 120 RPM, about 105 RPM to about 125 RPM, about 110 RPMto about 125 RPM, or about 100 RPM to about 125 RPM). The cells can beincubated, for example, in an incubator, such as a shake incubator withthrow (orbit) diameter of 25 mm or from about 3 mm to about 50 mm, whilechanging the RPM accordingly. After the first 48 to 96 hours of theperiod of time of incubation, continuously or periodically over theperiod of time, a first volume of the first liquid culture medium (e.g.,containing any mammalian cell concentration, e.g., a first volume offirst liquid culture medium which is or is made substantially free ofmammalian cells and/or microcarriers) is removed, and a second volume ofa second liquid culture medium is added to the first liquid culturemedium. Typically, the first and the second volumes are roughly equal,but can vary by a small amount, e.g., by up to about 10% when the firstand second volumes are compared. In some embodiments, the second volumeof the second liquid culture medium added is less (e.g., at most about1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% less) or more (e.g., at mostabout 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% more) than the firstvolume of the first liquid culture medium removed. As is known in theart, the term incubating can include short periods of time (e.g.,between 10 seconds and about 10 minutes, between 10 seconds and about 20minutes, between 10 seconds and about 30 minutes, between 10 seconds andabout 40 minutes, between about 10 seconds and about 50 minutes, orbetween 10 seconds and about 1 hour) in which a shake flask containingthe mammalian cell and liquid culture medium is removed from anincubator in order to remove the first volume of the first liquidculture medium and add the second volume of the second liquid culturemedium.

In another exemplary method, a shake flask is first provided. A firstliquid culture medium is added to the shake flask such that the mediumoccupies about 10% to about 40%, e.g., about 20% to about 30% (e.g.,about 20% to about 22%, about 22% to about 24%, about 24% to about 26%,about 26% to about 28%, about 28% to about 30%, about 20% to about 25%,or about 25% to about 30%) of the volume of the shake flask. At leastone mammalian cell and a plurality of microcarriers (a finalconcentration in the shake flask of about 1.0 g/L to about 15.0 g/L,e.g., a final concentration in the shake flask of between about 1.0 g/Lto about 2.5 g/L, about 1.0 g/L to about 2.0 g/L, about 1.0 g/L to about1.75 g/L, about 1.0 g/L to about 1.5 g/L, about 1.0 g/L to about 1.25g/L, about 2.5 g/L to 5.0 g/L, about 5.0 g/L to about 7.5 g/L, about 7.5g/L to about 10.0 g/L, about 10.0 g/L to about 12.5 g/L, about 12.5 g/Lto about 15.0 g/L, about 1.0 g/L to about 5.0 g/L, about 5.0 g/L toabout 10.0 g/L, about 10.0 g/L to about 15.0 g/L, about 2.5 g/L to about3.5 g/L, about 3.0 g/L to about 4.0 g/L, about 4.0 g/L to about 5.0 g/L,about 5.0 g/L to about 6.0 g/L, about 6.0 g/L to about 7.0 g/L, about7.0 g/L to about 8.0 g/L, about 8.0 g/L to about 9.0 g/L, about 9.0 g/Lto about 10.0 g/L, about 10.0 g/L to about 11.0 g/L, about 11.0 g/L toabout 12.0 g/L, about 12.0 g/L to about 13.0 g/L, about 13.0 g/L toabout 14.0 g/L, or about 14.0 g/L to about 15.0 g/L) is added to thefirst liquid culture medium, i.e., either before the medium is added tothe shake flask or afterward. As noted above, the addition of the liquidculture medium, a mammalian cell, and the liquid culture medium to theshake flask can occur in any order. Then, in a first time period, theshake flask is incubated at about 35° C. to about 39° C. (e.g., 35° C.to 37° C., 36° C. to 39° C., or 37° C. to 39° C.) with a rotaryagitation of about 85 RPM to about 125 RPM (e.g., about 85 RPM to about120 RPM, about 85 RPM to about 110 RPM, about 85 RPM to about 100 RPM,about 85 RPM to about 95 RPM, about 85 RPM to about 105 RPM, about 90RPM to about 110 RPM, about 95 RPM to about 115 RPM, about 100 RPM toabout 120 RPM, about 105 RPM to about 125 RPM, about 110 RPM to about125 RPM, or about 100 RPM to about 125 RPM). The cells can be incubated,for example, in an incubator, such as a shake incubator with throw(orbit) diameter from about 3 mm to about 50 mm. After about the first48 to 96 hours of the first time period, in each subsequent 24-hourperiod, (i) continuously or periodically removing a first volume of thefirst liquid culture medium that is substantially free of micro carriersfrom the shake flask, wherein the first volume is about 10% to about 95%(e.g., about 10% to 20%, about 20% to about 30%, about 30% to about 40%,about 40% to about 50%, about 50% to about 60%, about 60% to about 70%,about 70% to about 80%, about 80% to about 95%, about 50% to about 95%,about 50% to about 90%, or about 60% to about 90%) of the volume of thefirst liquid culture medium; and (ii) adding to the shake flask a secondvolume of a second liquid culture medium, wherein the first and secondvolume are about equal. As noted above, the first and the second volumesare roughly equal, but can vary by a small amount, e.g., by up to about10% when the first and second volumes are compared. Once the cellconcentration reaches about target cell density (e.g., about 1.0×10⁶cells/mL, about 1.5×10⁶ cells/mL, about 2.0×10⁶ cells/mL, about 2.2×10⁶cells/mL, about 2.4×10⁶ cells/mL, about 2.6×10⁶ cells/mL, about 2.8×10⁶cells/mL, about 3.0×10⁶ cells/mL, about 3.2×10⁶ cells/mL, about 3.4×10⁶cells/mL, about 3.6×10⁶ cells/mL, about 3.8×10⁶ cells/mL, about 4.0×10⁶cells/mL, about 1.0×10⁶ cells/mL to 4.0×10⁶ cells/mL, about 2.0×10⁶cells/mL to about 4.0×10⁶ cells/mL, about 2.0×10⁶ cells/mL to about4.0×10⁶ cells/mL, about 4.0×10⁶ cells/mL to about 6.0×10⁶ cells/mL,about 6.0×10⁶ cells/mL to about 8.0×10⁶ cells/mL, about 8.0×10⁶ cells/mLto about 10.0×10⁶ cells/mL, about 10.0×10⁶ cells/mL to about 15.0×10⁶cells/mL, about 15.0×10⁶ to about 20.0×10⁶ cells/mL, about 20.0×10⁶cells/mL to about 25.0×10⁶ cells/mL, about 25.0×10⁶ cells/mL to about30.0×10⁶ cells/mL, about 30.0×10⁶ cells/mL to about 35.0×10⁶ cells/mL,about 35.0×10⁶ cells/mL to about 40.0×10⁶ cells/mL, about 40.0×10⁶cells/mL to about 45.0×10⁶ cells/mL, or about 45.0×10⁶ cells/mL to about50.0×10⁶ cells/mL) the shake flask is incubated for a second time periodof about 2 days to about 7 days (e.g., about 2 days to about 4 days,about 3 days to about 5 days, about 4 days to about 6 days, and about 5days to about 7 days), at about 32° C. to about 39° C. (e.g., about 32°C. to about 35° C., about 32° C. to about 37° C., about 32° C. to about38° C., about 34° C. to about 39° C., about 34° C. to about 37° C.,about 35° C. to about 38° C., about 35° C. to about 39° C., about 36° C.to about 39° C., or about 37° C. to about 39° C.) with the rotaryagitation, and in each 24-hour period, performing steps (i) and (ii)described above, where the first and second liquid culture media used inthe first time period are of a substantially different type from thoseused in the second time period. Then, in a third period of time ofgreater than 2 days (e.g., 2, 3, 4, 5, 6, 7, 9, 10, 11, 12, 13, 14, 15,16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33,34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51,52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69,70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87,88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100 days, greaterthan 100 days, 110 days, 120 days, 130 days, 140 days, 150 days, 160days, 170 days, 180 days, 190 days, or 200 days, or at most 100 days,125 days, 150 days, 175 days, 200 days, 225 days, 250 days, 275 days, or300 days) incubating the shake flask at about 35° C. to about 39° C.(e.g., about 35° C. to about 37°, 36° C. to about 38° C., about 37° C.to about 39° C., or about 36° C. to about 39° C.) with the rotaryagitation, and in each 24-hour period, performing steps (i) and (ii)listed above, where the first and second liquid culture media used inthe second time period are of the same type as those used in the thirdtime period.

Various non-limiting examples of each aspect of these culturing methodsare described below. The exemplary aspects of the methods providedherein can be used in any combination without limitation.

Mammalian Cells

The methods provided herein can be used to culture a variety ofdifferent mammalian cells. In some examples of all the methods describedherein, the mammalian is an adherent cell. Non-limiting examples ofmammalian cells that can be cultured using any of the methods describedherein include: Chinese hamster ovary (CHO) cells (e.g., CHO DG44 cells,CHO-K1s cells, Sp2.0, myeloma cells (e.g., NS/0), B-cells, hybridomacells, T-cells, human embryonic kidney (HEK) cells (e.g, HEK 293E andHEK 293F), African green monkey kidney epithelial cells (Vero) cells,and Madin-Darby Canine (Cocker Spaniel) kidney epithelial cells (MDCK)cells. Additional mammalian cells that can be cultured using the methodsdescribed herein are known in the art. In non-limiting examples of anyof the methods described herein, the concentration of mammalian cellspresent in the shake flask at the start of any of the culturing methodsdescribed herein is about 0.1×10⁶ cells/mL to about 0.5×10⁶ cells/mL(e.g., about 0.25×10⁶ cells/mL to about 0.5×10⁶ cells/mL).

The mammalian cell can contain a recombinant nucleic acid (e.g., anucleic acid stably integrated in the mammalian cell's genome) thatencodes a recombinant protein (e.g., a recombinant protein that issecreted by the mammalian cell). Non-limiting examples of recombinantnucleic acids that encode exemplary recombinant proteins are describedbelow, as are recombinant proteins that are producible using the methodsdescribed herein. In some instances, the mammalian cell disposed in theshake flask for culturing is derived from a larger culture. For example,the mammalian cell in the shake flask can be derived from a large-scalebioreactor culture, i.e., a satellite culture can be prepared using anyof the methods described herein.

Culture Media

Liquid culture media are known in the art. The first and/or secondtissue culture medium (e.g., the first and second liquid culture mediumused in the first time period or the second and third time periods) canbe supplemented with a mammalian serum (e.g., fetal calf serum andbovine serum), and/or a growth hormone or growth factor (e.g., insulin,transferrin, and epidermal growth factor). Alternatively or in addition,the first and/or second liquid culture medium (e.g., the first and/orsecond liquid culture medium, e.g., the first and/or second liquidculture medium in the first time period or the second and third timeperiods) can be a chemically-defined liquid culture medium, ananimal-derived component free liquid culture medium, a serum-free liquidculture medium, or a serum-containing liquid culture medium.Non-limiting examples of chemically-defined liquid culture media,animal-derived component free liquid culture media, serum-free liquidculture media, and serum-containing liquid culture media arecommercially available.

A liquid culture medium typically contains an energy source (e.g., acarbohydrate, such as glucose), essential amino acids (e.g., the basicset of twenty amino acids plus cysteine), vitamins and/or other organiccompounds required at low concentrations, free fatty acids, and/or traceelements. The first and/or second liquid culture medium (e.g., the firstand/or second liquid culture medium used in the first time period or thesecond and third time periods) can, if desired, be supplemented with,e.g., a mammalian hormone or growth factor (e.g., insulin, transferrin,or epidermal growth factor), salts and buffers (e.g., calcium,magnesium, and phosphate salts), nucleosides and bases (e.g., adenosine,thymidine, and hypoxanthine), protein and tissue hydrolysates, and/orany combination of these or other additives.

Non-limiting examples of liquid culture media that are particularlyuseful in the presently described methods include, e.g., CD CHO, OptiCHO, and Forti CHO (all available from Life Technologies; Grand Island,N.Y.), Hycell CHO medium (Thermo Fisher Scientific, Inc.; Waltham,Mass.), Ex-cell CD CHO Fusion medium (Sigma-Aldrich Co.; St. Louis,Mo.), and PowerCHO medium (Lonza Group, Ltd.; Basel, Switzerland).Medium components that also may be useful in the present methodsinclude, but are not limited to, chemically-defined (CD) hydrolysates,e.g., CD peptone, CD polypeptides (two or more amino acids), and CDgrowth factors. Additional examples of liquid tissue culture medium andmedium components are known in the art.

Skilled practitioners will appreciate that the first liquid culturemedium and the second liquid culture medium described herein can be thesame type of media or different type of media. For example, in examplesof the methods that include a first time period, a second time period,and a third time period, the first and second liquid culture medium usedin the first time period are substantially different from the first andsecond liquid culture medium used in the second and third time period,and the first and second liquid culture medium used in the second andthird time period are substantially the same. For example, the first andsecond liquid culture medium used in the first time period can beselected from the group of a serum-containing liquid culture medium or aliquid culture medium that contains a mammalian protein or a mammalianprotein fraction or extract, and the first and second liquid culturemedium used in the second and third time periods can be selected fromthe group of: an animal-derived component free liquid culture medium, aserum-free liquid culture medium, a chemically-defined liquid culturemedium, and a protein-free liquid culture medium.

Microcarrier

In the methods described herein, a plurality of microcarriers is addedto the liquid culture medium (e.g., the first and/or second liquidculture medium). For example, the plurality of microcarriers can have anaverage diameter of between about 20 μm to about 1 mm (e.g., betweenabout 20 μm and about 250 μm, between about 100 μm to about 250 μm,between about 150 μm to about 250 μm, between about 250 μm and 500 μm,between about 200 μm to about 300 μm, between about 750 μm and 1 mm,between about 200 μm to about 800 μm, between about 200 μm and about 500μm, between about 500 μm and about 800 μm), where the microcarriers havea surface that is permissive or promotes attachment of a mammalian cell(e.g., any of the mammalian cells described herein or known in the art).In some examples, a microcarrier can contain one or more pores (e.g.,one or more pores with an average diameter of about 10 μm to about 100μm (e.g., between about 10 μm and 20 μm, about 20 μm to about 30 μm,about 30 μm to about 40 μm, about 50 μm to about 60 μm, about 60 μm toabout 70 μm, about 70 μm to about 80 μm, about 80 μm to about 90 μm,about 90 μm to about 100 μm, about 10 μm to about 45 μm, about 45 μm toabout 80 μm, about 25 μM to about 35 μm, or about 30 μm)). In someembodiments, the surface of the plurality of microcarriers and/or thesurface of the one or more pores in the plurality of microcarriers arecoated with an agent that promotes the attachment of a mammalian cell tothe microcarrier (e.g., attachment to the outer surface of themicrocarriers and/or the surface of the pores in the microcarrier).Examples of such agents that can be used to promote the attachment of amammalian cell include, but are not limited to, gelatin, collagen,poly-L-ornithine, polystyrene, and laminin.

In some examples, the microcarriers have an average effective cellbinding surface area of between about 0.5 m²/g dry and 2.0 m²/g dry(e.g., between about 0.75 m²/g dry and 1.25 m²/dry, between about 1.0m²/g dry and about 1.5 m²/dry, between about 1.25 m²/dry and about 1.5m²/dry, about 1.5 m²/dry and about 2.0 m²/dry, and about 1.1 m²/dry). Insome examples, the microcarriers have an average volume of about 10 mL/gdry to about 70 mL/g dry (e.g., about 10 mL/g dry to about 20 mL/g dry,about 20 mL/g dry to about 30 mL/g dry, about 30 mL/g dry to about 40mL/g dry, about 40 mL/g dry to about 50 mL/g dry, about 50 mL/g dry toabout 60 mL/g dry, about 60 mL/g dry to about 70 mL/g dry, about 10 mL/gdry to about 40 mL/g dry, about 30 mL/g dry to about 40 mL/g dry, about40 mL/g dry to about 70 mL/g dry, or about 40 mL/g dry). In someembodiments, the average relative density of the microcarriers isbetween 0.8 g/mL to about 1.2 g/mL (e.g., about 0.8 g/mL to about 0.9g/mL, about 0.9 g/mL to about 1.0 g/mL, about 1.0 g/mL to about 1.1g/mL, about 1.0 g/mL, about 1.1 g/mL to about 1.2 g/mL, about 0.95 g/mLto about 1.05 g/mL, or about 1.03 g/mL).

In some embodiments, the microcarriers are approximately spherical orellipsoidal in shape. In other examples, the microcarriers have anabraded or rough surface with small protuberances that increase thetotal outer surface area of the microcarrier. In some embodiments, themicrocarriers have a network structure. In some examples, themicrocarriers are hygroscopic. In some examples, the microcarrierscontain cellulose.

In some embodiments, the microcarriers have an outer surface and/or themicrocarrier pores have a surface that is positively charged (e.g.,positively charged due to the presence of N,N,-diethylaminoethylgroups). In some examples, the microcarriers have a network or net-likeor web-like structure. The microcarriers can have an average chargedensity of about 0.5 me/g to about 2.5 me/g (e.g., about 0.5 me/g toabout 1.5 meq/g, about 0.75 meq/g to about 1.25 meq/g, about 1.1 meq/g,about 1.5 meq/g to about 2.5 meq/g, about 1.5 meq/g to about 2.0 meq/g,about 1.8 meq/g, about 0.5 meq/g to about 1.0 meq/g, or about 1.0 meq/gto about 1.5 meq/g).

In some instances, the microcarrier can contain a natural polymer and/ora synthetic polymer. Non-limiting examples of synthetic polymers includepolyethylene glycol (PEG), polyethylene oxide, polyethyleneimine,diethyleneglycol, triethyleneglycol, polyalkalene glycol, polyalkalineoxide, polyvinyl alcohol, sodium polyphosphate, polyvinylpyrrolidone,polyvinylmethylether, polymethyloxazoline, polyethyloxazoline,polyhydroxypropyloxazoline, polyhydroxypropylmethacrylamide,polymethacrylamide, polydimethylacrylamide,polyhydroxypropylmethacrylate, polyhydroxyethylacrylate,hydroxymethylcellulose, hydroxyethylcellulose, polyglycerine,polyaspartamide, polyoxyethlene-polyoxypropylene copolymer (poloxamer),carboxylic acids (e.g., acrylic acid, methacrylic acid, itaconic acid,and maleic acid), polyoxyethylenes, polyethyleneoxide, unsaturatedethylenic monodicarboxylic acids, polylactic acid (PLA), polypropyleneoxide, poly(lactide-co-glycolide) (PLGA), poly(epsilon-caprolactone),poly(ethylethylene), polybutadiene, polyglycolide, polymethylacrylate,polyvinylbutylether, polystyrene, polycyclopentadienylmethylnorbornene,polyethylenepropylene, polyethylethylene, polyisobutylene, polysiloxane,methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate,isobutyl acrylate, 2-ethyl acrylate, t-butyl acrylate, methacrylates(e.g., ethyl methacrylate, n-butyl methacrylate, and isobutylmethacrylate), acrylonitriles, methacrylonitrile, vinyls (e.g., vinylacetate, vinylversatate, vinylpropionate, vinylformamide,vinylacetamide, vinylpyridines, and vinyllimidazole), aminoalkyls (e.g.,aminoalkylacrylates, aminoalkylsmethacrylates, andaminoalkyl(meth)acrylamides), styrenes, polyalkalene glycol,polyalkaline oxide, and lactic acids. Non-limiting examples of naturalpolymers include cellulose, lecithin, and hyaluronic acid. Amicrocarrier can contain a mixture of different polymers (e.g., anycombination of one or more polymers described herein or known in theart) in the same or different ratios. Any of the microcarriers describedherein can contain a core containing one or more polymers (e.g., any ofthe polymers described herein or known in the art) and an outer layerthat contains one or more different polymers (e.g., any of the polymersdescribed herein or known in the art).

Non-limiting exemplary microcarriers that can be used in any of themethods described herein include CytoPore™ 1 and CytoPore™ 2 (availablefrom GE Healthcare, Life Sciences, Piscataway, N.J.). Additionalexamples of microcarriers that can be used in any of the methodsdescribed herein are publicly available and known in the art.

Shake Flasks

The shake flask can be sterile and have a volume between about 125 mL toabout 3 L (e.g., a 3-L, a 2.5-L, a 2-L, a 1.5-L, a 1-L, a 750-mL, a500-mL, 400-mL, 300-mL, 250-mL, 200-mL, 150-mL, or 125-mL shake flask).The shake flask can have a volume, for example, of about 250 mL to about300 mL, about 300 mL to about 400 mL, about 400 mL to about 500 mL,about 500 mL to about 600 mL, about 600 mL to about 700 mL, about 700 mLto about 800 mL, about 800 mL to about 900 mL, about 900 mL to about 1L, about 100 mL to about 500 mL, about 500 mL to about 1 L, about 600 mLto about 1 L, about 1 L to about 3 L, about 1 L to about 2 L, about 2 Lto about 3 L, about 1.5 L to about 2.5 L. The shake flask can include atleast one gas permeable surface (e.g., at least one surface having a gaspermeable membrane which may also act as a sterile barrier) and/or atleast one vented cap. A shake flask may have on its outer surface astructure that allows the shake flask to be stably placed in a tissueculture incubator (e.g., a rotary incubator).

The interior surface of the shake flask may have at least one coating(e.g., at least one coating of gelatin, collagen, poly-L-ornithine,polystyrene, and laminin). Exemplary shake flasks that can be used inany of the methods described herein can be purchased from Corning Inc.(Tewsbury, Mass.), Presens (Brondby, Denmark), Nalge-Nunc International(Rochester, N.Y.). Exemplary shake flasks include T-flasks, Erlenmeyerflasks, or any art-recognized modified versions thereof. Additionalexamples of shake flasks (e.g., different shapes and dimensions of shakeflasks) and interior surface coatings of shake flasks are known in theart and can be used in the present methods.

Agitation

The methods described herein involve the agitation of the culturecontaining the mammalian cell, a plurality of microcarriers, and thefirst and/or second liquid culture medium. The agitation can occur at afrequency of at about 85 RPM to about 125 RPM (e.g., about 85 RPM toabout 120 RPM, about 85 RPM to about 110 RPM, about 85 RPM to about 100RPM, about 85 RPM to about 95 RPM, about 85 RPM to about 105 RPM, about90 RPM to about 110 RPM, about 95 RPM to about 115 RPM, about 100 RPM toabout 120 RPM, about 105 RPM to about 125 RPM, about 110 RPM to about125 RPM, about 100 RPM to about 125 RPM, about 95 RPM to about 105 RPM,about 95 RPM to about 105 RPM, about 105 RPM to about 115 RPM, or about115 RPM to about 125 RPM) (e.g., in an incubator, such as a shakeincubator with throw (orbit) diameter from about 3 mm to about 50 mm).

As can be appreciated in the art, the level of agitation (e.g., RPMspeed) can be varied depending upon the size and shape of the shakeflask (e.g., the diameter of the shake flask), the throw (orbit)diameter of the incubator that is used to perform the agitation, and theaverage size, shape, density, and concentration of the plurality ofmicrocarriers. For example, a smaller throw (orbit) diameter can requirea higher level of agitation (e.g., a higher RPM speed), while a largerthrow (orbit) diameter can require a lower level of agitation (e.g., alower RPM speed) to achieve the conditions necessary to achieve optimalviable cell density and recombinant protein production. In anotherexample, a shake flask having a larger diameter can require a lower RPMspeed, while a shake flask having a smaller diameter can require ahigher RPM speed to achieve the conditions necessary to achieve optimalviable cell density and recombinant protein production. The frequency ofagitation can be varied depending on cell culture conditions, e.g., theconcentration, density, and/or the size and/or surface shape of themicrocarriers. As one skilled in the art can appreciate, ifmicrocarriers present in the first and/or second liquid culture medium(e.g., the first and/or second liquid culture medium used in the first,second, and third time periods) have a high mass, a high density, alarge outer surface area, or a relatively high velocity, the sheerforces generated by such microcarriers can have a negative impact oncell viability and recombinant protein production in the culture. Inaddition, those in the art can appreciate that the rate of agitationshould be high enough to avoid substantial and/or undesirable settlingof the microcarriers on the bottom of shake flask.

In some embodiments, the incubating is performed using a rotaryincubator with a throw (orbit) diameter of between about 25 mm to about50 mm and an agitation of between about 85 RPM to about 125 RPM (e.g.,about 85 RPM to about 120 RPM, about 85 RPM to about 110 RPM, about 85RPM to about 100 RPM, about 85 RPM to about 95 RPM, about 85 RPM toabout 105 RPM, about 90 RPM to about 110 RPM, about 95 RPM to about 115RPM, about 100 RPM to about 120 RPM, about 105 RPM to about 125 RPM,about 110 RPM to about 125 RPM, about 100 RPM to about 125 RPM, or anyof the RPM ranges described herein). In some embodiments, the incubatingis performed using a rotary incubator with a throw (orbit) diameter ofabout 3 mm to about 25 mm and an agitation of about 85 RPM to about 125RPM (e.g., about 85 RPM to about 120 RPM, about 85 RPM to about 110 RPM,about 85 RPM to about 100 RPM, about 85 RPM to about 95 RPM, about 85RPM to about 105 RPM, about 90 RPM to about 110 RPM, about 95 RPM toabout 115 RPM, about 100 RPM to about 120 RPM, about 105 RPM to about125 RPM, about 110 RPM to about 125 RPM, about 100 RPM to about 125 RPM,or any of the other RPM ranges described herein).

Agitation can be performed, e.g., using rotary circular shaking at afrequency of about 85 RPM to about 125 RPM (e.g., about 85 RPM to about120 RPM, about 85 RPM to about 110 RPM, about 85 RPM to about 100 RPM,about 85 RPM to about 95 RPM, about 85 RPM to about 105 RPM, about 90RPM to about 110 RPM, about 95 RPM to about 115 RPM, about 100 RPM toabout 120 RPM, about 105 RPM to about 125 RPM, about 110 RPM to about125 RPM, about 100 RPM to about 125 RPM, or any of the RPM rangesdescribed herein). Alternatively or in addition, the shake flask can beagitated using a rotary ellipsoidal shaking, or horizontal and/orvertical tilting of the shake flask. The agitation can be performedcontinuously or periodically.

The agitation can be performed using a humidified atmosphere controlledincubator (e.g., at a humidity of about or greater than 20%, e.g., aboutor greater than 30%, 40%, 50%, 60%, 70%, 75%, 80%, 85%, 90%, or 95%, ora humidity of 100%) with a mechanical device that provides the agitationof one or more of the shake flasks containing the mammalian cell, theplurality of microcarriers, and a liquid culture medium (e.g., the firstand/or second liquid culture medium, and the first and/or second liquidculture medium used in one or more of the first, second, and third timeperiods).

Reactor Angle

In some embodiments, the shake flask can be incubated at a reactor angleof about 25 degrees to about 90 degrees (e.g., about 25 degrees to about55 degrees, about 25 degrees to about 90 degrees, about 35 degrees toabout 90 degrees, about 45 degrees to about 90 degrees, or about 35 toabout 65 degrees) from horizontal. For example, the shake flask can beplaced at a reactor angle of about 60 degrees to about 85 degrees fromhorizontal, about 70 degrees to about 85 degrees from horizontal, about25 degrees to about 60 degrees, about 25 degrees to about 55 degrees,about 30 degrees to about 55 degrees from horizontal, about 40 degreesto about 55 degrees horizontal, or about 40 degrees to about 50 degreesfrom horizontal. The shake flask may be placed at a reactor angle ofabout 45 degrees from horizontal to about 50 degrees from horizontal, orfrom about 40 degrees from horizontal to about 45 degrees fromhorizontal. The shake flask may be placed in a device that specificallyand securely positions the shake flask at a reactor angle of about 25degrees to about 90 degrees from horizontal (e.g., specificallypositions the container at a reactor angle of about 25 degrees to about90 degrees, about 35 degrees to about 90 degrees, about 45 degrees toabout 90 degrees, about 35 degrees to about 65 degrees, or about 40degrees to about 55 degrees from horizontal). The positioning of theshake flask can be performed using any means known in the art, e.g.,through the use of a brace or a locking element.

Temperature

The culturing methods described herein can be performed at a temperatureof 32° C. to about 39° C., e.g., about 32° C. to about 37° C. Forexample, in some methods the shake flask can be incubated at atemperature of about 37° C. from the beginning to the end of the culturerun. Some examples of the methods described herein include a first timeperiod during which the shake flask is incubated at a temperature ofabout 35° C. to about 39° C., e.g., about 35° C. to about 37° C., asecond time period during which the shake flask is incubated at about32° C. to about 39° C., e.g., about 32° C. to about 37° C., and thirdtime period during which the shake flask is incubated at about 35° C. toabout 39° C., e.g., about 35° C. to about 37° C. Skilled practitionerswill appreciate that the temperature can be changed at specific timepoint(s) in the culturing method (e.g., during one or more of the firsttime period, the second time period, and the third time period), e.g.,on an hourly or daily basis. For example, the temperature can be changedor shifted (e.g., increased or decreased) at about one day, two days,three days, four days, five days, six days, seven days, eight days, ninedays, ten days, eleven days, twelve days, fourteen days, fifteen days,sixteen days, seventeen days, eighteen days, nineteen days, or abouttwenty days or more after the initial seeding of the shake flask withthe mammalian cell) or at any time point within the first, second,and/or third time periods described herein. For example, the temperaturecan be shifted upwards (e.g., a change of up to or about 0.1, 0.2, 0.3,0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5,5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, or 10.0° C.). Forexample, the temperature can be shifted downwards (e.g., a change of upto or about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.5, 2.0,2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0,9.5, or 10° C.).

Culture Medium Removal and Replacement

The methods described herein include removing from the shake flask afirst volume of a first liquid culture medium (e.g., containing anyconcentration of mammalian cells and any recombinant protein, e.g., afirst volume of a first liquid culture medium that is substantially freeof cells and/or microcarriers), and adding to the shake flask a secondvolume of a second liquid culture medium, wherein the first volume andthe second volume are about equal. Removal and adding can be performedsimultaneously or sequentially, or a combination of the two. Further,removal and adding can be performed continuously (e.g., at a rate thatremoves and replaces a volume of between 0.1% to 800% (e.g., between 1%and 700%, between 1% and 600%, between 1% and 500%, between 1% and 400%,between 1% and 350%, between 1% and 300%, between 1% and 250%, between1% and 100%, between 100% and 200%, between 5% and 150%, between 10% and50%, between 15% and 40%, between 8% and 80%, and between 4% and 30%) ofthe volume of the shake flask or the first liquid culture medium volumeover any given time period (e.g., over a 24-hour period, over anincremental time period of about 1 hour to about 24 hours, or over anincremental time period of greater than 24 hours)) or periodically(e.g., once every third day, once every other day, once a day, twice aday, three times a day, four times a day, five times a day, or more thanfive times a day), or any combination thereof. Where performedperiodically, the volume that is removed or replaced (e.g., within abouta 24-hour period, within an incremental time period of about 0.1 hour toabout 24 hours, or within an incremental time period of greater than 24hours) can be, e.g., between 0.1% to 800% (e.g., between 1% and 700%,between 1% and 600%, between 1% and 500%, between 1% and 400%, between1% and 300%, between 1% and 200%, between 1% and 100%, between 100% and200%, between 5% and 150%, between 10% and 50%, between 15% and 40%,between 8% and 80%, and between 4% and 30%) of the volume of the shakeflask or the first liquid culture medium volume. The first volume of thefirst liquid culture medium removed and the second volume of the secondliquid culture medium added can in some instances be held approximatelythe same over each 24-hour period (or, alternatively, an incrementaltime period of about 0.1 hour to about 24 hours or an incremental timeperiod of greater than 24 hours) over the entire or part of theculturing period. As is known in the art, the rate at which the firstvolume of the first liquid culture medium is removed (volume/unit oftime) and the rate at which the second volume of the second liquidculture medium is added (volume/unit of time) can be varied. The rate atwhich the first volume of the first liquid culture medium is removed(volume/unit of time) and the rate at which the second volume of thesecond liquid culture medium is added (volume/unit of time) can be aboutthe same or can be different.

Alternatively, the volume removed and added can change (e.g., graduallyincrease) over each 24-hour period (or alternatively, an incrementaltime period of between 0.1 hour and about 24 hours or an incrementaltime period of greater than 24 hours) during the culturing period. Forexample the volume of the first liquid culture medium removed and thevolume of the second liquid culture medium added within each 24-hourperiod (or alternatively, an incremental time period of between about 1hour and above 24 hours or an incremental time period of greater than 24hours) over the culturing period can be increased (e.g., gradually orthrough staggered increments) over the culturing period from a volumethat is between 0.5% to about 20% of the shake flask volume or the firstliquid culture medium volume to about 25% to about 150% of the shakeflask volume or the first liquid culture medium volume.

In some examples of the methods described herein, after the first 48 to96 hours of the culture period, in each 24-hour period, the first volumeof the first liquid culture medium removed (e.g., in the first, second,and/or third time period) and the second volume of the second liquidculture medium added (e.g., in the first, second, and/or third timeperiod) is about 10% to about 95% (e.g., about 10% to about 20%, about10% to about 20%, about 20% to about 30%, about 30% to about 40%, about40% to about 50%, about 50% to about 60%, about 60% to about 70%, about70% to about 80%, about 80% to about 90%, about 85% to about 95%, about60% to about 80%, or about 70%) of the volume of the first liquidculture medium.

Skilled practitioners will appreciate that the first liquid culturemedium and the second liquid culture medium can be the same type ofmedia. In other instances, the first liquid culture medium and thesecond liquid culture medium can be substantially different. In someembodiments that include a first time period, second time period, andthird time period, the first and second liquid culture media used in thefirst time period are a substantially different type of media comparedto the first and second liquid culture media used in the second timeperiod, and the first and second liquid culture media used in the secondtime period are the same type of media compared to the first and secondliquid culture media used in the third time period. As can be recognizedin the art, the first and second liquid culture media used in the firsttime period do not have to be exactly the same (as long as they are thesame type of culture medium); any of the first and second liquid culturemedia used in the second time period and/or third time period do nothave to be exactly the same (again, as long as they are the same type ofmedium and a substantially different media type from the first andsecond liquid culture medium used in the first time period).

The first volume of the first liquid culture medium can be removed,e.g., by centrifuging (e.g., slow-speed swinging bucket centrifugation)the shake flask or using any other automated system, and removing thefirst volume of the first liquid culture (e.g., a first volume of thefirst liquid culture medium that is substantially free of cells and/ormicrocarriers) from the supernatant. Alternatively or in addition, thefirst volume of the first liquid culture medium can be removed byseeping or gravity flow of the first volume of the first liquid culturemedium through a sterile membrane with a molecular weight cut-off thatexcludes the mammalian cell and/or microcarriers. Alternatively or inaddition, the first volume of the first liquid culture medium can beremoved by stopping or significantly decreasing the rate of agitationfor a period of at least 10 seconds (e.g., at least 30 seconds, 40seconds, 50 seconds, 1 minutes, 2 minutes, 3 minutes, 4 minutes, 5minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 40minutes, 50 minutes, or 1 hour) and removing or aspirating the firstvolume of the first liquid culture medium from the top of the shakeflask (e.g., removal from a part of the liquid culture medium where themicrocarriers have not settled due to gravitational force). The shakeflask may be placed in an incubator during the period in which theagitation is ceased. One skilled in the art will understand that theshake flask may be removed from the incubator for a short period of time(e.g., less than 30 minutes, 20 minutes, 15 minutes, 10 minutes, 8minutes, 6 minutes, 4 minutes, 2 minutes, or 1 minute) while the firstliquid culture medium is removed from the shake flask.

The second volume of the second liquid culture medium can be added tothe first liquid culture medium, e.g., by perfusion pump. The secondliquid culture medium can be added to the first liquid culture mediummanually (e.g., by pipetting the second volume of the second liquidculture medium directly onto the first liquid culture medium) or in anautomated fashion.

In some instances, removing the first volume of the first liquid culturemedium (e.g., a first volume of the first liquid culture medium that issubstantially free of mammalian cells and/or microcarriers) and addingto the first liquid culture medium a second volume of the second liquidculture medium does not occur within at least 1 hour (e.g., within 2hours, within 3 hours, within 4 hours, within 5 hours, within 6 hours,within 7 hours, within 8 hours, within 9 hours, within 10 hours, within12 hours, within 14 hours, within 16 hours, within 18 hours, within 24hours, within 36 hours, within 48 hours, within 72 hours, within 96hours, or after 96 hours) of the seeding of the shake flask with amammalian cell.

CO₂

Methods described herein can further include incubating the shake flaskin an atmosphere containing at most or about 1% to 15% CO₂ (e.g., atmost or about 14% CO₂, 12% CO₂, 10% CO₂, 8% CO₂, 6% CO₂, 5% CO₂, 4% CO₂,3% CO₂, 2% CO₂, or at most or about 1% CO₂). Moreover, any of themethods described herein can include incubating the shake flask in ahumidified atmosphere (e.g., at least or about 20%, 30%, 40%, 50%, 60%,70%, 85%, 80%, 85%, 90%, or at least or about 95% humidity, or about100% humidity).

Exemplary Devices

Non-limiting examples of devices that can be used to perform theculturing methods described herein include: Appropriate TechnicalResources (Maryland, USA) distributes INFORS Multiron shake incubator(INFORS; Basel, Switzerland), and Kuhner shake incubator (Kuhner AG;Basel, Switzerland). Non-limiting examples of devices that can be usedto perform the culturing methods include a rotary incubator with a throw(orbit) diameter of between about 3 mm to about 50 mm (e.g., betweenabout 1 mm and about 25 mm, or between about 25 mm and about 50 mm).Additional examples of shake incubators are known in the art.

Methods of Producing a Recombinant Protein

Also provided herein are methods of producing a recombinant protein,which include culturing a cell that is capable of producing therecombinant protein using a method described herein. Followingperformance of the method, the recombinant protein can be recovered fromthe mammalian cell (e.g., the mammalian cell that is attached to themicrocarrier) and/or from the first or second culture medium (e.g., thefirst and/or second liquid culture medium used in one or more of thefirst, second, and third time periods). In some embodiments, therecombinant protein is recovered from the first and/or second liquidculture medium at any given time point during the culturing method(e.g., recovered from the first and/or second liquid culture medium onone or more of days 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32,33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50,51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68,69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86,87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100 of culture,or after more than 100 days of culture, or at any time point during oneor more of the first time period, the second time period, and the thirdtime period).

Skilled practitioners will appreciate that any of the various cultureparameters (e.g., shake flasks, volumes, rates or frequencies ofreplacing culture volumes, agitation frequencies, type of microcarrier,temperatures, media, and CO₂ concentrations) can be used in anycombination to perform these methods. Further, any of the mammaliancells described herein or known in the art can be used to produce arecombinant protein.

A nucleic acid encoding a recombinant protein can be introduced into amammalian cell using a wide variety of methods known in molecularbiology and molecular genetics. Non-limiting examples includetransfection (e.g., lipofection), transduction (e.g., lentivirus,adenovirus, or retrovirus infection), and electroporation. In someinstances, the nucleic acid that encodes a recombinant protein is notstably integrated into a chromosome of the mammalian cell (transienttransfection), while in others the nucleic acid is integrated.Alternatively or in addition, the nucleic acid encoding a recombinantprotein can be present in a plasmid and/or in a mammalian artificialchromosome (e.g., a human artificial chromosome). Alternatively or inaddition, the nucleic acid can be introduced into the cell using a viralvector (e.g., a lentivirus, retrovirus, or adenovirus vector). Thenucleic acid can be operably linked to a promoter sequence (e.g., astrong promoter, such as a β-actin promoter and CMV promoter, or aninducible promoter). A vector containing the nucleic acid can, ifdesired, also contain a selectable marker (e.g., a gene that confershygromycin, puromycin, or neomycin resistance to the mammalian cell).

In some instances, the recombinant protein is a secreted protein and isreleased by the mammalian cell into the extracellular medium (e.g., thefirst and/or second liquid culture medium, e.g., the first and/or secondliquid culture medium used in one or more of the first, second, andthird time periods). For example, a nucleic acid sequence encoding asoluble recombinant protein can contain a sequence that encodes asecretion signal peptide at the N- or C-terminus of the recombinantprotein, which is cleaved by an enzyme present in the mammalian cell,and subsequently released into the extracellular medium (e.g., the firstand/or second liquid culture medium, or the first and/or second liquidculture medium used in one or more of the first, second, and third timeperiods). In other instances, the recombinant protein is a solubleprotein that is not secreted, and the recombinant protein is recoveredfrom within the mammalian cell (e.g., from within the mammalian cellthat is attached to the microcarrier, e.g., recovered from the mammaliancell attached to the microcarrier after it has been unattached from themicrocarrier).

Non-limiting examples of recombinant proteins that can be produced bythe methods provided herein include immunoglobulins (including light andheavy chain immunoglobulins, antibodies, or antibody fragments (e.g.,any of the antibody fragments described herein), enzymes (e.g., agalactosidase (e.g., an alpha-galactosidase), Myozyme, or Cerezyme),proteins (e.g., human erythropoietin, tumor necrosis factor (TNF), or aninterferon alpha or beta), or immunogenic or antigenic proteins orprotein fragments (e.g., proteins for use in a vaccine). In someembodiments, the recombinant protein is an engineered antigen-bindingpolypeptide that contains at least one multifunctional recombinantprotein scaffold (see, e.g., the recombinant antigen-binding proteinsdescribed in Gebauer et al., Current Opin. Chem. Biol. 13:245-255, 2009;and U.S. Patent Application Publication No. 2012/0164066 (hereinincorporated by reference in its entirety)). Non-limiting examples ofrecombinant proteins that are antibodies include: panitumumab,omalizumab, abagovomab, abciximab, actoxumab, adalimumab, adecatumumab,afelimomab, afutuzumab, alacizumab, alacizumab, alemtuzumab, alirocumab,altumomab, amatuximab, anatumomab, apolizumab, atinumab, tocilizumab,basilizimab, bectumomab, belimumab, bevacizumab, biciromab, canakinumab,cetuximab, daclizumab, densumab, eculizumab, edrecolomab, efalizumab,efungumab, ertumaxomab, etaracizumab, golimumab, infliximab,natalizumab, palivizumab, panitumumab, pertuzumab, ranibizumab,rituximab, tocilizumab, and trastuzumab. Additional examples oftherapeutic antibodies that can be produced by the methods describedherein are known in the art. Additional non-limiting examples ofrecombinant proteins that can be produced by the present methodsinclude: alglucosidase alfa, laronidase, abatacept, galsulfase, lutropinalfa, antihemophilic factor, agalsidase beta, interferon beta-la,darbepoetin alfa, tenecteplase, etanercept, coagulation factor IX,follicle stimulating hormone, interferon beta-la, imiglucerase, dornasealfa, epoetin alfa, and alteplase.

A secreted, soluble recombinant protein can be recovered from the liquidculture medium (e.g., the first and/or second liquid culture medium,e.g., the first and/or second liquid culture medium used in one or moreof the first, second, and third time periods) by removing or otherwisephysically separating the liquid culture medium from microcarriers andtheir associated mammalian cells. A variety of different methods forremoving liquid culture medium from mammalian cells are known in theart, including, for example, centrifugation, filtration, pipetting,and/or aspiration. The secreted recombinant protein can then berecovered and further purified from the liquid culture medium using avariety of biochemical techniques including various types ofchromatography (e.g., affinity chromatography, molecular sievechromatography, cation exchange chromatography, or anion exchangechromatography) and/or filtration (e.g., molecular weight cut-offfiltration).

To recover an intracellular recombinant protein, the mammalian cell(e.g., the mammalian cell attached to the microcarrier) can be lysed. Insome examples, the mammalian cell is released from the surface of themicrocarrier before it is lysed. Methods for releasing an adherent cellfrom the surface of a microcarrier are known in the art (e.g., vortexingor agitation). In other examples, the mammalian cell is lysed while itis still attached to the microcarrier (e.g., using any of the exemplarymethods listed below).

A wide variety of methods for lysing mammalian cells are known in theart, including, for example, sonication and/or detergent, enzymatic,and/or chemical lysis. A recombinant protein can be purified from amammalian cell lysate using a variety of biochemical methods known inthe art, typically starting with a step of centrifugation to remove thecellular debris, and then one or more additional steps (e.g., one ormore types of chromatography (e.g., affinity chromatography, molecularsieve chromatography, cation exchange chromatography, or anion exchangechromatography) and/or filtration (e.g., molecular weight cut-offfiltration)).

In some embodiments, the recovered recombinant protein is at least orabout 50% pure by weight, e.g., at least or about 55% pure by weight, atleast 60% pure by weight, at least 65% pure by weight, at least 70% pureby weight, at least 75% pure by weight, at least 80% pure by weight, atleast 85% pure by weight, at least 90% pure by weight, at least 95% pureby weight, at least 96% pure by weight, at least 97% pure by weight, atleast 98% pure by weight, or at least or about 99% pure by weight, orgreater than 99% pure by weight.

In some embodiments, the recovered recombinant protein is a recombinanthuman protein that has one or more different biophysical properties ascompared to the same native protein in a human (e.g., differences in thetype or amount of glycosylation, differences in phosphorylation,differences in acylation, differences in metallation or metalstoichiometry, and/or differences in cofactor binding).

Also provided herein is a recombinant protein produced by any of themethods described herein.

Methods for Testing a Manufacturing Process

Also provided herein are methods for testing a manufacturing process formaking a recombinant protein. These methods include performing a methodof producing a recombinant protein described herein and, during themethod and/or afterward, detecting or measuring at least one (e.g., two,three, four, five, six, seven, eight, nine, ten, or eleven) culturereadout (e.g., the recombinant protein in the cell or in the firstand/or second culture medium (e.g., the first and/or second liquidculture medium used in one or more of the first, second, and third timeperiods), glucose consumption, viable cell concentration, lactateproduction, volumetric productivity, lactate yield from glucose,glutamine concentration, glutamate concentration, pH of culture medium,partial pressure or concentration of dissolved CO₂, concentration orpartial pressure of dissolved O₂, metabolite mass transfer, andmetabolite mass balance); and comparing the at least one culture readoutto a reference level of the at least one (e.g., two, three, four, five,six, seven, eight, nine, ten, or eleven) culture readout (e.g., areference level of the recombinant protein in the cell or in the firstand/or second culture medium (e.g., the first and/or second liquidculture medium used in one or more of the first, second, and third timeperiods), glucose consumption, viable cell concentration, lactateproduction, volumetric productivity, lactate yield from glucose,glutamine concentration, glutamate concentration, pH of culture medium,concentration or partial pressure of dissolved CO₂, concentration orpartial pressure of dissolved O₂, metabolite mass transfer, andmetabolite mass balance).

Skilled practitioners will appreciate that any of the various cultureparameters (e.g., shake flasks, volumes, type of microcarrier, rates orfrequencies of replacing culture volumes, agitation frequencies,temperatures, media, and CO₂ exposure) described herein can be used inany combination to perform these methods. Further, any of the mammaliancells described herein or known in the art can be used in the methods.

The reference level of the at least one culture readout (e.g., level ofrecombinant protein in the cell or in the first and/or second culturemedium (e.g., the first and/or second liquid culture medium used in oneor more of the first, second, and third time periods), glucoseconsumption, viable cell concentration, lactate production, volumetricproductivity, lactate yield from glucose, glutamine concentration,glutamate concentration, pH of culture medium, concentration or partialpressure of dissolved CO₂, concentration or partial pressure ofdissolved O₂, metabolite mass transfer, and metabolite mass balance) canbe a level produced using a different culturing method, e.g., aculturing method that utilizes at least one different culture parameter(e.g., a different first and/or second liquid culture medium (e.g., adifferent first and/or second liquid culture medium in one or more ofthe first, second, or third time periods), a different mammalian cell, adifferent frequency and/or type of agitation, a different type orconcentration of microcarrier, a different batch re-feed or perfusionrate (e.g., 10% to 95% of the shake flask volume or the first liquidculture medium volume over each 24-hour time period after the first 48to 96 hours of culture), and any of the other culture parametersdescribed herein).

The methods described herein can be used to test the effect of anycomponent or feature of a manufacturing process. For example, the methoddescribed herein can be used to test the effect of different rawmaterials, microcarriers, agitation levels, shake flasks, anti-clumpingagents, culture media (e.g., chemically-defined culture media), ornutrient elements or compounds on the at least one culture readout(e.g., any of the culture readouts described herein, e.g., the effect onrecombinant protein production and/or mammalian cell growth). Forexample, provided herein are methods of testing the efficacy of a firstor second liquid culture medium, a raw ingredient or supplement presentin a first or second liquid culture medium, or a source of a mammaliancell for use in a method of producing a recombinant protein that includeproviding a shake flask containing a mammalian cell disposed in a firstliquid culture medium, wherein the first liquid culture medium occupiesabout 10% to about 40%, e.g., about 20% to about 30% of the volume ofthe shake flask, and contains a plurality of microcarriers at aconcentration of about 1.0 g/L to about 15.0 g/L; incubating the shakeflask for a period of time at about 31° C. to about 40° C., e.g., about32° C. to about 37° C., and with a rotary agitation of about 85revolutions per minute (RPM) to about 125 RPM; and after about the first48 to 96 hours of the period of time, continuously or periodicallyremoving a first volume of the first liquid culture medium and adding tothe first liquid culture medium a second volume of a second liquidculture medium, wherein the first and second volumes are about equal;detecting or determining at least one culture readout (e.g., any of theculture readouts described herein, e.g., the recombinant protein in thecell or in the first and/or second culture medium); comparing the atleast one culture readout to a reference level of the at least oneculture readout (e.g., any of the culture readouts described herein,e.g., recombinant protein in the cell or in the first and/or secondliquid culture medium) produced by a different culturing method thatuses one or more of a different first or second liquid culture medium, adifferent raw ingredient or supplement present in the first or secondliquid culture medium, or a different source of a mammalian cell; andidentifying the first or second liquid culture medium, the rawingredient or supplement present in the first or second liquid culturemedium, or the source of the mammalian cell that is associated withbeneficial change (e.g., increase or decrease) in the at least oneculture readout (e.g., an increased amount of recombinant protein) ascompared to the reference level as being efficacious for use in a methodof producing a recombinant protein. For example, an increase inrecombinant protein level, an increase in viable cell concentration, anincrease in volumetric productivity, and an increase in glucoseconsumption compared to the reference level indicates that the first orsecond liquid culture medium, the raw ingredient or supplement presentin a first or second liquid culture medium, or the source of themammalian cell are efficacious for use in a method of producing arecombinant protein.

The methods described herein can also be used to test the effect ofchanging any of the various cell culture parameters described herein orknown in the art (e.g., the volume or shape of a shake flask, thefrequency of agitation, the sheer force generated by the plurality ofmicrocarriers in the first and/or second liquid culture medium, theculture seeding density, the pH of the first and/or second liquidculture medium (e.g., the pH of the first and/or second liquid culturemedium used in one or more of the first, second, or third time periods),dissolved O₂ concentration or partial pressure, the inner surfacecoating of the shake flask, one or more of the concentration, size,shape, surface properties, density, and porosity of the microcarriers,the various ingredients within a liquid culture media (e.g., the firstand/or second liquid culture media, e.g., the first and/or second liquidculture medium used in one or more of the first, second, and third timeperiods), the amount and/or type of agitation, the mammalian cell typeor line, dissolved CO₂ concentration or partial pressure, thetemperature, the volume of liquid culture medium (e.g., the volume ofthe first and/or second liquid culture media), and/or the rate orfrequency of removing the first volume of the first liquid culturemedium and adding the second volume of the second liquid culture mediumto the first culture medium (e.g., the rate or frequency of removing thefirst volume of the first culture medium and adding the second volume ofthe second liquid culture medium in one or more of the first, second,and third time periods). The methods can also be used to test thequality of water used to prepare the liquid culture medium (e.g., thefirst and/or second liquid culture medium, e.g., the first and/or secondliquid culture medium used in one or more of the first, second, andthird time periods) and/or the effect of different trace metals in theliquid culture medium on at least one culture readout on at least oneculture readout (e.g., any of the culture readouts described herein,e.g., the effect on recombinant protein production and/or mammalian cellgrowth). The methods can also be used to test the effect of a growthfactor or growth hormone (e.g., the effect of the presence of a growthfactor or growth hormone in the first time period) on at least oneculture readout (e.g., any of the culture readouts described herein,e.g., the effect on recombinant protein production and/or mammalian cellgrowth). The method can also be used to test filtration processes andfilters used to prepare the first and/or second liquid culture medium(e.g., the first and/or second liquid culture medium used in one or moreof the first, second, and third time periods). The method can also beused to test liquid culture medium stability and the effect of a liquidculture medium on at least one culture readout (e.g., any of the culturereadouts described herein, e.g., the effect on recombinant proteinproduction and/or mammalian cell growth). The method can also be used toscreen various recombinant cells lines and cell banks for their abilityto produce a desired recombinant protein (e.g., a desired secretedtherapeutic protein). As noted herein, the method can also be used toscreen any cell culture process parameter, including but limited to, thetype and frequency of agitation, sheer force generated by themicrocarriers, perfusion rate and volume, culture seeding density, andothers.

The method described herein can also be used to test for the presence ofa contaminant in a first or second liquid culture medium, a raw materialused to generate a first or second liquid culture medium, or a source ofa mammalian cell. For example, provided herein are methods of testingfor the presence of a contaminant in a first or second liquid culturemedium, raw materials used to generate a first or second liquid culturemedium, or a source of a mammalian cell that include providing a shakeflask containing a mammalian cell disposed in a first liquid culturemedium, wherein the first liquid culture medium occupies about 10% toabout 40%, e.g., about 20% to about 30% of the volume of the shakeflask, and contains a plurality of microcarriers at a concentration ofabout 1.0 g/L to about 15.0 g/L; incubating the shake flask for a periodof time at about 32° C. to about 39° C., e.g., about 32° C. to about 37°C., and with a rotary agitation of about 85 revolutions per minute (RPM)to about 125 RPM; and after about the first 48 to 96 hours of the periodof time, continuously or periodically removing a first volume of thefirst liquid culture medium and adding to the first liquid culturemedium a second volume of a second liquid culture medium, wherein thefirst and second volumes are about equal; detecting or determining atleast one culture readout (e.g., any of the culture readouts describedherein, e.g., the recombinant protein in the cell or in the first and/orsecond culture medium); comparing the at least one culture readout to areference level of the at least one culture readout (e.g., any of theculture readouts described herein, e.g., amount of recombinant proteinpresent in the cell or in the first and/or second culture medium)produced by a different culturing method that uses one or more of adifferent first or second liquid culture medium, different raw materialsto generate the first or second liquid culture medium, or a differentsource of the mammalian cell; and identifying the first or second liquidculture medium, the raw materials used to generate the first or secondliquid culture medium, or the source of a mammalian cell as containing acontaminant when the level of the at least one culture parameter isdetrimentally changed (e.g., increased or decreased) compared to thereference level. For example, a decrease in recombinant proteinproduction (e.g., a decrease in recombinant protein in the cell or inthe first and/or second culture medium), volumetric productivity, orviable cell concentration as compared to the reference level is adetrimental change that indicates the presence of a contaminant in thefirst or second liquid culture medium, a raw material used to generatethe first or second liquid culture medium, or the source of themammalian cell. Some methods further include one or more assays todetermine the identity of the contaminant present in the first or secondliquid culture medium, the raw material used to generate the first orsecond liquid culture medium, or the source of the mammalian cell. Thecontaminant can be a biological contaminant (e.g., a mycobacterium, afungus, a bacterium, a virus, or an undesired mammalian cell). Thecontaminant can be an inorganic contaminant. The contaminant can also bea physically uncharacterized substance.

The methods can used to conduct high throughput cell culture experimentsto perform a design-of-experiment (DOE) or a quality-by-design (QBD)optimization of cell culturing methods. For example, provided herein aremethods of optimizing a manufacturing process of producing a recombinantprotein that include providing a shake flask containing a mammalian celldisposed in a first liquid culture medium, wherein the first liquidculture medium occupies about 10% to about 40%, e.g., about 20% to about30%, of the volume of the shake flask, and contains a plurality ofmicrocarriers at a concentration of about 1.0 g/L to about 15.0 g/L;incubating the shake flask for a period of time at about 32° C. to about39° C., e.g., about 32° C. to about 37° C., and with a rotary agitationof about 85 revolutions per minute (RPM) to about 125 RPM; and afterabout the first 48 to 96 hours of the period of time, continuously orperiodically removing a first volume of the first liquid culture mediumand adding to the first liquid culture medium a second volume of asecond liquid culture medium, wherein the first and second volumes areabout equal; detecting at least one culture readout (e.g., any of theculture readouts described herein, e.g., amount of recombinant proteinin the cell or in the first and/or second culture medium); comparing theat least one culture readout to a reference level of the at least oneculture readout (e.g., any of the culture readouts described herein,e.g., amount of recombinant protein present in the cell or in the firstand/or second culture medium) produced by a different culturing method;and identifying and removing or altering in a manufacturing process anyculture components or parameters that are associated with a detrimentalchange (e.g., increase or decrease) in the at least one culture readout(e.g., any of the culture readouts described herein, e.g., amount ofrecombinant protein produced) as compared to the reference level of theat least one culture readout (e.g, any of the culture readouts describedherein, e.g., recombinant protein produced), or identifying and addingto a manufacturing process any culture components or parameters that areassociated with a beneficial change (e.g., increase or decrease) in theat least one culture readout (e.g., any of the culture readoutsdescribed herein, e.g., amount of recombinant protein produced) ascompared to the reference level of the at least one culture readout(e.g., any of the culture readouts described herein, e.g., recombinantprotein produced). For example, an increase in the amount of recombinantprotein produced, volumetric productivity, or viable cell concentrationis a beneficial change in a culture readout, and a decrease in theamount of recombinant protein produced, volumetric productivity, orviable cell concentration is a detrimental change in a culture readout.In some instances, the method is used to identify in a high throughputfashion, optimized cell culture conditions that can be used forup-scaled (e.g., bioreactor) production of a recombinant protein.

In any of the methods described in this section, the reference level ofthe at least one culture readout can be from a larger-scale culture(e.g., a perfusion bioreactor, e.g., a 2000-L perfusion bioreactor, 40-Lperfusion bioreactor, or a 12-L perfusion bioreactor). In someembodiments of any of the methods described in this section, themammalian cell is cultured in a shake flask using any of the methodsdescribed herein over the same time period that a larger-scale cultureis performed (cultured in parallel). For example, the inoculum used toinoculate the shake flask in any of the methods described herein is alsoused to inoculate a larger-scale perfusion bioreactor at approximatelythe same time.

In one embodiment, the inoculum that is used to seed the shake flask isobtained from a larger-scale culture (e.g., a larger-scale perfusionbioreactor). For example, an aliquot from a larger-scale culture (e.g.,an aliquot from a larger-scale perfusion bioreactor) is removed from thelarger-scale culture at any time point (e.g., removed during the growthphase, the transition phase, or the harvest phase described herein) andused to inoculate the shake flask (e.g., used to start a satellite shakeflask culture). An aliquot can be removed from the larger-scale cultureduring the growth phrase and used to inoculate or seed a shake flaskcontaining a liquid culture medium and a plurality of microcarriers(e.g., as described herein), and the shake flask is then incubated underconditions that replicate or are similar to the growth phase conditionsemployed in the larger-scale culture. An aliquot can alternatively, oradditionally, be removed from the larger-scale culture during thetransition phase and used to inoculate or seed a shake flask containinga liquid culture medium and a plurality of microcarriers (e.g., asdescribed herein), and the shake flask is then incubated underconditions that replicate or are similar to the transition phaseconditions employed in the larger-scale culture. An aliquot canalternatively, or additionally, be removed from the larger-scale cultureduring the harvest phase and used to inoculate or seed a shake flaskcontaining a liquid culture medium and a plurality of microcarriers(e.g., as described herein), and the shake flask is then incubated underconditions that replicate or are similar to the harvest phase conditionsemployed in the larger-scale culture. In any of these methods, one ormore culture parameters can be altered in the methods used to culturethe mammalian cell in the shake flask (as compared to the cultureparameters or components used to culture the mammalian cell in thelarger-scale culture), at least one culture readout is measured, and theat least one culture readout is compared to the at least one culturereadout determined for the larger-scale culture. As can be appreciatedby those in the art, these methods can be used to test the effect of aspecific culture parameter or component on at least one culture readoutduring one or more specific phases in the culturing process (e.g., theeffect of one or more culture parameters and/or culture component(s) onat least one culture readout during the growth, transition, and/orharvest phase).

In certain embodiment, these methods can also be performed to determinewhether a contaminant is present in the larger-scale bioreactor, bydetermining or detecting at least one culture readout in the shake flaskculture, comparing the at least one culture readout to a reference levelof the at least one culture readout (e.g., a level of the at least oneculture readout from a culture that is substantially free ofcontamination), and identifying the larger-scale bioreactor ascontaining a contaminant when the at least one culture readout in theshake flask culture as compared to the reference level of the at leastone culture readout indicates that a contaminant is present in the shakeflask. The contaminant can be, for example, a biological contaminant,such as a virus, a fungus, an undesired mammalian cell, or a bacterium,such as a mycobacterium. The contaminant can be, for example, avesivirus.

EXAMPLES

The invention is further described in the following examples, which donot limit the scope of the invention described in the claims.

Example 1 Exemplary Culture Methods using a Shake Flask andMicrocarriers

The human recombinant form of human alpha-galactosidase can be producedusing established recombinant engineering techniques in a CHO cell line.The current manufacturing production of recombinant humanalpha-galactosidase utilizes a 2000-L continuous perfusion microcarriercell culture process technology. Typically the production cell cultureprocess includes three phases: a growth, transition, and harvest phase.There is a demand for a high throughput cell culture process system thatwould accurately model the cell culture process conditions achieved in a2000-L bioreactor cell culture process run. Described in this Example isa shake flask microcarrier batch re-feed cell culture process thatsimulates the recombinant human alpha-galactosidase 2000-L bioreactorperfusion cell culture process.

Materials and Methods

Recombinant Human Alpha-Galactosidase Cell Culture

The cells used for the experiments are stably transformed with a nucleicacid that encodes a secreted form of human recombinantalpha-galactosidase. A growth medium (925 medium with 10% DBS, pH 7.3,and 0.1% Pluronic F-68) was used during the cell bank culture expansionprocess.

Equipment

A Multitron Shaker incubator (Appropriate Technical Resources, Inc.,Model number AG CH-4103) was used to culture the cells. A BeckmanCoulter Vi-Cell XR Cell Viability Analyzer (Model number XR, Cat#731050) was used to measure the viable cell density and percentage ofviable cells in the culture.

Methods

The inoculum used for the exemplary shake flask microcarrier batchre-feed cell culture process runs was generated from a seed cultureexpansion of a thawed vial of recombinant humanalpha-galactosidase-producing CHO cells. After five days of expansion ofthe thawed cells in 925 medium with 10% DBS, pH 7.3, and 0.1% PluronicF-68, the seed culture was used to inoculate a shake flask (at a finalconcentration of 0.25×10⁶ viable cells/mL in the shake flask) containinga sterilized microcarrier slurry (CytoPore2, GE Healthcare, Piscataway,N.J.; final concentration of 1.5 g/L; average size 200-280 μm; averagepore size 30 μm) and growth medium (925 medium with 6% DBS, pH 7.0, and0.1% Pluronic F-68), which initiates the growth phase of the cellculture. The cultures were maintained at 37° C. or 36° C., 95 RPM, 80%relative humidity, and 5% CO₂. When the culture reached a target celldensity of between 2.5×10⁶ to 3.0×10⁶ viable cells/mL, the transitionphase was initiated by changing the liquid culture medium to a differentproduction liquid culture medium (925 medium, pH 6.85-7.05, and 0.1%Pluronic F-68) and shifting the temperature to 32° C. After 5 days oftransition phase, the temperature was shifted back to 37° C. or 36° C.,and the cultures were maintained with production liquid culture medium.Medium exchange was initiated on the third day of the growth phase andwas continued until the end of culture, with a daily batch re-feedexchange of 70% of the initial volume of the liquid culture mediumpresent in the shake flask at the start of the culture. On each day,starting on the third day of the growth phase, medium exchange wasperformed by briefly stopping the agitation of the shake flask, allowingthe microcarriers to settle to the bottom of the shake flask in abiosafety hood. In some instances, the shake flask was placed in a rackwhich positions the shake flask at a 45 degree angle with respect to thehorizon or the benchtop while the microcarriers settled to the bottom ofthe shake flask in order to improve medium exchange. A non-limitingexample of such a rack is shown in FIG. 1. After the microcarriers havesettled to the bottom of the shake flask, a volume of liquid culturemedium that is 70% of the initial volume of the liquid culture mediumpresent in the shake flask is removed from the shake flask, and thenshortly thereafter, a volume of liquid culture medium that issubstantially the same volume as the volume of liquid culture mediumremoved is added to the shake flask. On pre-determined culture days, thefollowing culture parameters were analyzed: viable and suspension celldensity and the percentage of viable of cells, pCO₂, pO₂, pH, glucoseand lactate concentration, and glutamine and glutamate concentration.Titer samples were collected and kept at −20° C. until the assay wasperformed to measure the recombinant human alpha-galactosidase activity.A total of two full cell culture process runs were performed using atriplicate set of flasks for each run. The average and standarddeviation of the resulting data were calculated and are shown in each ofFIGS. 2-6.

Results and Discussion

Growth Phase Duration and Transition Density

Cell culture performance during the growth phase is critical to thesuccessful production of a recombinant protein. Table 1 provides asummary of the growth phase duration and viable cell density achieved atthe end of the growth phase of two shake flask microcarrier batchre-feed cell process runs that were started with the inoculum describedabove. The growth phase duration was consistent between the two cellculture process runs, with a viable cell density of 2.5×10⁶ cells/mL to3.0×10⁶ cells/mL (an exemplary target viable cell density range forbeginning the transition phase) achieved after 8 days of growth.

TABLE 1 Summary of growth phase duration and viable cell density at thebeginning of the transition phase for two recombinant humanalpha-galactosidase shake flask microcarrier batch re-feed cell cultureprocess runs. Transition Density Experiment Growth Duration (E6 viablecells/mL) Replicate CCCD-HT-03 192 hours (G8) 2.6 +/− 0.5 n = 3CCCD-HT-11 195 hours (G8) 2.9 +/− 0.4 n = 3

Cell Culture Growth

The growth and health performance of the cell culture were monitoredthrough several difference metrics. Culture growth was tracked by themeasurement of the viable cell concentration (FIG. 2). The resultingdata show a consistent increase in cell concentration through growthphase and early transition phase, and the achievement of a maximumviable cell concentration of approximately 3.0×10⁶ cells/mL at the endof the growth phase. As the culture is adapting to serum-free medium(starting at the beginning of transition phase through the harvestphase), there is a slight decrease in viable cell concentration duringthe early harvest phase. The culture thereafter stabilizes and maintainsa viable cell concentration of between 2.0×10⁶ and 4.0×10⁶ for most ofthe harvest phase, with further increase in viable cell density duringthe late harvest phase. Throughout most of harvest phase, the percentageof viable cells is greater than 80% (FIG. 3).

Cell detachment was also monitored throughout the cell culture processruns by measuring the suspended cell concentration in the culture (FIG.4). The suspended cell concentration in the culture peaked at thebeginning of the harvest phase, most likely due to the effect of serumwithdrawal on the cells. The suspended cell concentration remained low(between 0.1×10⁶ to 0.3×10⁶ cells/mL) throughout the cell cultureprocess runs.

Culture Productivity

Volumetric productivity (units/L/day) was monitored throughout the cellculture process runs to gain an understanding of the productivityperformance of the shake flask microcarrier batch re-feed model. Asshown in FIG. 5, culture productivity peaked at the late transitionphase/early harvest phase. However, as the culture adapts to the lack ofserum, a sharp decline in productivity is observed. The cell culturerecovers from this trough period in early harvest phase, with theculture productivity improving throughout the harvest phase. Abouthalf-way into the harvest phase (around day 20 of the harvest phase),the cell culture productivity maintains a steady level (with volumetricproductivity rate (VPR) above 600 units/L/day) until the end of run. Itis noted that there was not a trough period in viable cell concentration(FIG. 2) that corresponds to the trough period observed for cell cultureproductivity.

When comparing the productivity profile of this exemplary shake flaskmicrocarrier batch re-feed process to the 2000-L process, twodistinctive differences are observed. First, the productivity peakduring the late transition phase/early harvest phase is higher in the2000-L process when compared to the exemplary shake flask microcarrierbatch re-feed process. Second, the trough period for the 2000-L processis delayed to the mid-harvest phase rather than during the early harvestphase seen in the exemplary shake flask microcarrier batch re-feedprocess. The recovery in culture productivity following the trough isalso slower in the 2000-L process than in the exemplary shake flaskmicrocarrier batch re-feed process. These performance differences may beattributed to the difference in the medium exchange methods used in thetwo cell culture processes. Medium exchange in the 2000-L perfusionprocess is conducted in a continuous manner, where the cells arecontinuously exposed to conditioned/fresh medium. On the other hand,medium exchange in the exemplary shake flask microcarrier batch re-feedmodel described in this Example is conducted once a day, where 70% ofthe volume of the first liquid culture medium is removed and replacedwith about the same volume of a second liquid culture medium in a bolusfashion. However, the cumulative volumetric productivity in theexemplary shake flask cell culture process run described in this Exampleand the 2000-L bioreactor cell culture process run show a similar trend(FIG. 6).

Culture Metabolism

Cellular metabolism was monitored during the cell culture process runsthrough glucose and lactate concentration measurements. The glucoseconsumption rate and lactate production rate were calculated fromglucose and lactate analysis of the harvest phase samples. Lower lactatelevels during the harvest phase indicates efficient glucose usage by thecultured cells. Overall, both glucose consumption and lactate productionwere consistent with the cell growth profile (FIG. 2). The most dynamicperiods of the culture occurred at two different culture stages: i)where cell proliferation occurs with serum-containing medium, and ii)towards the end of the harvest phase, where a re-growth period occurs(noted by an increase in both viable cell density and metabolicactivity). Glutamine and glutamate concentration profiles indicate adecline in glutamine consumption and glutamate production during theearly harvest phase, which corresponds to the observed trough period.

Culture pH, pCO₂, and pO₂

Culture pH, pCO₂, and pO₂ profiles were monitored using the blood gasanalyzer during sampling. Both the pH and pO₂ profiles were consistentwith the viable cell concentration profile. The pCO₂ profile shows thatpCO₂ levels were maintained between 30-35 mmHg, which correspond to the5% CO₂ setting of the incubator.

Summary of Results

The exemplary recombinant alpha-galactosidase shake flask microcarrierbatch re-feed cell culture process runs described in this Exampleachieve several beneficial results, e.g., the achievement of atransition cell density of 2.5×10⁶ viable cells/mL to 3.0×10⁶ viablecells/mL in only 7-9 days, the maintenance of a viable cellconcentration of between 2.0×10⁶ cells/mL to 6.0×10⁶ cells/mL throughthe harvest phase, the achievement of a low suspended cell concentration(<0.5×10⁶ cells/mL) throughout the culture process (with the exceptionof a short period of elevated suspended cell concentration shortly afterthe serum is removed from the culture), and achievement of cultureproductivity peaks late in the transition phase. It is noted that whilethe culture productivity does undergo a short trough during earlyharvest phase, the recovery from this trough is prompt, with avolumetric productivity above 600 units/L/day throughout the harvestperiod.

The degree of variability of shake flask microcarrier cell cultureprocess runs can be attributed to small differences in liquid culturemedium/raw materials and experimental variability. However, the cultureperformance trends should be similar. This exemplary shake flaskmicrocarrier batch re-feed process has been used for several otherapplications, such as satellite cultures in support of bioreactor runs(40-L and 2000-L cell culture process runs), trace metal and transitiontemperature studies on the production of recombinant humanalpha-galactosidase, and cell culture process understanding anddevelopment.

As will be appreciated by one skilled in the field of biotechnology, theexemplary shake flask microcarrier batch re-feed process used for theproduction of recombinant alpha-galactosidase described in this Examplecan be extended to other applications, such as testing and designingimprovements to a cell culture process, and monitoring ortrouble-shooting a manufacturing process. The small scale shake flaskmicrocarrier processes described herein will also allow for theminimization of resources and materials required for the largerbioreactor processes.

Example 2 Experiments to Determine the Effect of MicrocarrierConcentration and Frequency of Agitation on Viable Cell Concentration inShake Flasks

A set of experiments were performed in order to test the effect ofdifferent microcarrier concentrations with different frequencies ofagitation on mammalian cell culture growth performance in shake flasks.

Methods

The cells were cultured under the growth phase conditions described inExample 1, except that different concentrations of microcarriers anddifferent frequencies of rotary agitation were used.

The culture used to inoculate the shake flasks containing themicrocarriers was prepared by placing a thawed cell bank into two 250-mLsize shake flasks with 50 mL growth medium. The resulting seed cultureswere incubated in shake flasks at 37° C., 125 RPM, 6% CO₂, and 80%relative humidity until they were used to inoculate shake flaskscontaining the microcarriers. Following inoculation, the shake flaskscontaining microcarriers were cultured using the parameters set forthbelow. In all the experiments, 925 medium with 10% Dulbecco's bovineserum, pH 7.0, 0.1% Pluronic F-68 was used.

TABLE 2 Cell Culture Conditions Culture A B Scale 250 mL, smooth shakeflask, 60 mL working volume Ucarrier type CytoPore 2 CytoPore 2[carrier], g/L 1.0, 1.5, 2.0 1.0, 1.5, 2.0 Seeding density 0.25 × 10⁶viable cells/mL G-phase Medium 925 medium with 925 medium with 10% serum10% serum Temp (C.) 37 C. 37 C. Agitation (RPM) 125 or 85 % RH 80% #Replicates 2

The microcarriers were prepared in phosphate buffered saline andautoclaved. The resulting sterilized microcarriers were then added intoeach shake flask under sterile conditions to reach a final concentrationin each cell flask of 1 g/L, 1.5 g/L, or 2 g/L. The shake flaskmicrocarrier cultures were then cultured for 6 days, and the viable celldensity was determined over time.

Results

The data in FIG. 7 show that mammalian cells can grow in shake flaskscontaining microcarriers when agitated at a frequency of 85 RPM or 125RPM. The data also show that when a frequency of agitation of 85 or 125RPM is used, shake flasks containing 1.0 g/L and 1.5 g/L microcarriershave a higher viable cell density.

Example 3 Shake Flask Culture as a Model of a 40-L Bioreactor Process

This study was designed to explore use of the shake flask culturingmethods described herein for satellite culture of a 40-L recombinanthuman alpha-galactosidase bioreactor, and to compare the performance andproduction achieved in the satellite shake flask cultures to theperformance and production achieved in a 40-L bioreactor culture.

Procedures

Scale-Down Model Description

The 40-L bioreactor used in these experiments is a stainless steel,stirred tank vessel developed to mimic a 2000-L manufacturing productionbioreactor. This fully-automated vessel is steam-in-place sterilized,and has a control infrastructure and utility configuration similar to a2000-L production bioreactor.

The 250-mL satellite shake flask culture utilizes a disposablegamma-sterilized Corning non-pyrogenic polycarbonate Erlenmeyer flaskwith a vented cap. The satellite shake flask culture is incubated in anAppropriate Technical Resources, Inc. (ATR) incubator with CO₂,humidity, and temperature controlled. The ATR incubator both controlsand monitors the environmental conditions of the satellite shake flaskcultures.

Methods

40-L Bioreactor Culture

The 40-L recombinant human alpha-galactosidase bioreactor culturessampled for this study were inoculated with two working cell banks:09TP040 and 09TP038. Recombinant cells that contain a nucleic acidencoding recombinant human alpha-galactosidase were initially grown insuspension culture until used to inoculate a 40-L bioreactor containingCytopore II microcarriers at a final concentration of 1.5 g/L. The cellswere cultured in a 10% serum-containing medium and stepped down to 6%serum-containing medium at the N−1 stage. The cells were cultured in 6%serum-containing medium until the completion of the growth phase in the40-L bioreactors. Serum-containing growth medium was removed andreplaced at a rate of 1.2 RV/day for 120 hrs at the completion of growthphase in order to transition the 40-L bioreactor cultures to serum-freeproduction medium. The 40-L bioreactors were operated to model a 2000-Lproduction bioreactor with controlled parameters (dissolved oxygen, pH,temperature, and pCO₂) maintained within manufacturingspecifications/ranges and physical parameters (perfusion rate,agitation, sparger gas exit velocity, and cone flush rate) were scaledto match a 2000-L bioreactor with the exception of nitrogen sparge,overlay concentration, and surface area to volume.

Multiple experimental conditions were investigated in the 40-Lbioreactors in the satellite shake flask culture studies. The 40-Lbioreactor cultures sampled for the harvest phase satellite culturesused the cell line WCB 09TP040, and were operated with and without theaddition of Trace A Elements (Invitrogen) to the serum-free productionmedium. The non-Trace A Elements 40-L bioreactor culture data wasincluded in the comparisons with the satellite shake flask culture datadue to its similar performance to both the Trace A Elements 40-Lbioreactor culture data and the satellite shake flask culture data. The40-L bioreactor cultures sampled for the growth phase satellite culturesused the cell line WCB 09TP038 and irradiated serum in the growthmedium.

250 mL Shake Flask Satellite Cultures

The 250-mL satellite shake flask cultures were started at two timepoints during the recombinant human alpha-galactosidase 40-L bioreactorculture: growth phase and harvest phase (FIG. 8). A sterile 250-mL livecell culture microcarrier-containing sample was removed from the 40-Lbioreactor cultures using a sample port. Well-mixed culture from thissample was then sterile transferred to either a 250-mL shake flask or asterile flat-bottom container with a stir bar used to pool culture frommultiple reactors. If the culture was pooled first, a well-mixed samplefrom this pool was then transferred to a 250-mL shake flask. Once theculture has been transferred to the 250-mL shake flask, a sample wastaken for cell counts, metabolites, and titer. After sampling, ifperfusion was ongoing in the 40-L bioreactor cultures, a re-feed wasperformed on the shake flasks and then they were transferred to an ATRshaker incubator.

Satellite shake flask culture working volume and incubator rotationalRPM were varied. The working volume was reduced from an initial 68 mL to60 mL, and then to 50 mL. The weight of the flask was checked on day 0after the inoculation, and then checked daily to verify that flaskvolume remained constant after batch re-feed. The frequency of rotationwas increased from 95 RPM to 110 RPM to determine if more efficientmixing would have a beneficial effect on culture performance. It wasobserved in previous experiments that at 95 RPM, microcarriers tended toconcentrate to the center of the 250-mL shake flask, whereas at 110 RPM,there was a more even distribution of microcarriers throughout the shakeflask. The harvest phase satellite shake flask cultures were agitated ata constant frequency throughout the experiment. The growth phasesatellite shake flask cultures, independent of condition, were initiallystarted at 85 RPM, and then ramped up to 95 RPM on growth day 3. Thisagitation strategy was chosen to minimize the shear stress on thesecultures during the first few days of adaption to the shake flask growthconditions, and then increased to provide adequate mixing.

The ATR incubator was maintained at 5.0% CO₂, 37° C., and 80% relativehumidity (RH) for all satellite shake flask cultures. The 5.0% CO₂concentration was not comparable to the 40-L bioreactor culture CO₂concentrations, but it was selected due to the lack of pH control andease of operation. The temperature of the satellite shake flask cultureswas left at a standard incubator temperature of 37° C. instead ofmatching the 40-L bioreactor culture temperature of 36° C. This wasassumed to not have a large effect on satellite shake flask cultureperformance.

To reproduce the growth conditions of the 40-L perfusion bioreactorcultures in the satellite shake flask cultures, a 0.7× flask volumebatch re-feed was performed daily to replace spent medium with freshmedium. Batch re-feeding was accomplished by tilting and holding the250-mL shake flask at a 45° angle with a specialized rack. Thecell-attached/containing microcarriers were allowed to settle for ˜1minute, and the spent media was removed and replaced with fresh medium.The fresh medium was stored at 4° C. before use and equilibrated to 5.0%CO₂ and 37° C. in a 250-mL shake flask in an ATR shaker incubator for˜1-3 hours before re-feed. All of the satellite shake flask cultureswere sampled before the daily re-feed, every 2-3 days, for pH, pO₂, andpCO₂ (Bayer 248 Blood Gas Analyzer), viable cell density (Vicell XR),percentage of viable cells (viable cells/total cells; Vicell XR),metabolite concentration (glucose, lactate, glutamine, glutamate; YSI2700), Apoptosis (Guava Nexin Assay), and titer of recombinant humanalpha-galactosidase.

The harvest phase satellite shake flask cultures were sampled from two40-L bioreactors: IDs P403-38 and P407-33. The 40-L bioreactor cultureswere operated with Trace A Elements (Invitrogen) addition to theproduction media. Three harvest phase satellite cultures were started onharvest day 2 from culture removed from the P407-33 bioreactor culture,and directly transferred to three 250-mL shake flasks at a workingvolume of 68 mL. Two harvest phase satellite shake flask cultures werestarted on harvest day 4 from culture removed from the P403-38bioreactor culture, and two satellite harvest phase shake flask cultureswere started on harvest day 4 from culture removed from the P407-33bioreactor culture. The samples removed from these 40-L bioreactorcultures were directly transferred to the four 250-mL harvest phasesatellite shake flask cultures at a working volume of 60 mL withoutbeing pooled. All harvest phase satellite shake flask cultures weresampled post-transfer, and then a re-feed was performed at 0.7× shakeflask volume before being placed into an ATR incubator. The medium usedin the harvest phase satellite shake flask cultures was a different lotnumber than the medium used in the 40-L bioreactor cultures, but was thesame composition and contained 1× Trace A Elements (Invitrogen). Theseharvest phase satellite shake flask cultures were maintained until theend-of-process (harvest day 53).

The culture for the growth phase satellite shake flask cultures wassampled from two 40-L bioreactor cultures: IDs P405-29 and P408-29 atpost-inoculation by ˜1 hour on G0 (day of inoculation). The two 40-Lbioreactor culture samples were pooled, and then transferred to four250-mL shake flasks at two working volumes (Table 3). Batch re-feed wasstarted on G4, a day later than the start of the 40-L perfusionbioreactor culture (G3), due to a day of lag observed in satellite shakeflask culture cell counts and metabolite consumption. These growth phasesatellite shake flask cultures were maintained from G0-G8, but wereterminated in early harvest phase due to a transition deviationresulting in a high transition cell density outside of the acceptablerange and an extra day at 37° C. Only the growth data is used from thisexperiment.

TABLE 3 Conditions for 250-mL Shake Flask Satellite Study ExperimentalIncubator Phase Duration Conditions Conditions Growth G0-G8 Condition 1:5.0% CO₂, 37° C., Phase 60 mL w/v, and 80% RH 95 RPM Condition 2: 50 mLw/v, 95 RPM Harvest H2-H53 Condition 1: 5.0% CO₂, 37° C., Phase 68 mLw/v, and 80% RH 95 RPM Condition 2: 60 mL w/v, 95 RPM Condition 3: 60 mLw/v, 110 RPM

Results

Growth Phase Satellite Cultures

The viable cell growth for all conditions in the growth phase satelliteshake flask cultures lagged due to transfer stress and agitationchanges, but after recovery, viable cell growth was similar to the 40-Lparent bioreactor cultures grown in parallel (FIG. 9). There was aninitial day of cell growth lag in the growth phase satellite shake flaskcultures. This growth lag is most likely caused by the stress on theculture during the transfer process from the 40-L bioreactor cultures.It has also been previously observed that the shake flask model requiresadditional days of growth to reach a transition density of 3.0×10⁶cells/mL. An additional day of lag was observed when the agitation waschanged on growth day 2 from 85 RPM to 95 RPM. A larger effect wasobserved in the 50-mL growth phase satellite shake flask cultures. Thislag was also observed in the culture viability data (FIG. 10), and isthought to be a result of additional shear stress due to the smallerworking volume to flask volume ratio for the 50-mL growth phasesatellite shake flask cultures. The increased shear stress most likelyresulted in the increased suspension cell concentration in the 50-mLgrowth phase satellite shake flask cultures (FIG. 11).

Production in all conditions in the growth phase satellite shake flaskcultures trended similar to the 40-L parent bioreactor cultures grown inparallel (FIG. 12). The lower titer observed in the growth phasesatellite shake flask cultures was due to lower cell concentration.Specific production was initially slightly higher in the growth phasesatellite shake flask cultures, but converged with the 40-L bioreactorculture data as the growth phase satellite shake flask culturesrecovered (FIG. 13). The 50-mL growth phase satellite shake flaskcultures had a lower titer compared to the 68-mL growth phase satelliteshake flask cultures due to lower cell concentration, which wassupported by similar specific production of recombinant humanalpha-galactosidase between the two types of growth phase satelliteshake flask cultures (FIG. 13).

The glucose, lactate, glutamate, and glutamine metabolism of the growthphase satellite shake flask cultures initially trended similar to thedata from the 40-L bioreactor cultures, but started to deviate on day 5.The glucose and glutamine concentration in the growth phase satelliteshake flask cultures increased with the first batch re-feed on day 3,and then declined as cell growth continued, and lactate productionincreased outside of the 40-L bioreactor culture range. Lactateproduction was higher in the growth phase satellite shake flask cultureson day 5, and then remained higher than the 40-L bioreactor cultures.The yield of lactate to glucose for the growth phase satellite shakeflask cultures remained similar to the 40-L bioreactor cultures, whichsuggested that glucose/lactate metabolism was similar in the growthphase satellite shake flask cultures and the 40-L bioreactor cultures(FIG. 14). Glutamate concentration deviated from the 40-L bioreactorcultures in the growth phase satellite shake flask cultures, and thenappeared to converge on day 8. The 40-L bioreactor cultures had atemperature reduction on growth day 5, which suppressed cell metabolismand growth. There was not a similar temperature shift in the growthphase satellite shake flask cultures, which caused the deviation inmetabolism on growth day 8. Higher lactate production in the growthphase satellite shake flask cultures resulted in the deviation ofglucose and glutamine on day 5. Lactate production was suppressed in the50-mL growth phase satellite shake flask cultures compared to the 60-mLgrowth phase satellite shake flask cultures, but this was most likely aresult of the lower cell density in this culture.

The pH in the growth phase satellite shake flask cultures was initiallysimilar to the 40-L bioreactor cultures, but deviated on day 3 due tolack of active pH control and remained lower than the 40-L bioreactorcultures due to higher lactate production. The 40-L bioreactor culturesused NaOH addition to maintain the pH above 6.80. The growth phasesatellite shake flask culture pH increased back into range of the 40-Lbioreactor cultures on day 4 due to a re-feed on day 3 whichsuppressed/diluted lactate. The pO₂ and pCO₂ in the growth phasesatellite shake flask cultures were very different from the 40-Lbioreactor cultures due to the lack of active control for theseparameters. The pCO₂ was lower in the growth phase satellite shake flaskcultures due to more efficient sweep and a 5.0% CO₂ incubator set point.The pO₂ is higher in the growth phase satellite shake flask culturesthan the 40-L bioreactor cultures, but decreases as cell growthincreases in the growth phase satellite shake flask cultures. The highercell mass in the 60-mL growth phase satellite shake flask cultures wasrepresented by a lower pO₂.

Harvest Phase Satellite Shake Flask Cultures

Viable cell growth for all conditions in the harvest phase satelliteshake flask cultures was similar to the 40-L parent bioreactor culturesgrown in parallel (FIG. 15). There was an initial drop in viable cellconcentration in 2-3 days after being transferred to the 250-mL harvestphase satellite shake flask culture. This drop was more pronounced inthe 60-mL harvest phase satellite shake flask cultures. This drop was6-8 days earlier than the corresponding viable cell concentration troughin the recombinant human alpha-galactosidease 40-L bioreactor cultures(FIG. 15). Viability in the harvest phase satellite shake flask culturesfollowed the same trend as the 40-L bioreactor cultures, and decreasedin the harvest phase satellite shake flask cultures during the troughperiod (FIG. 16). This viable cell concentration trough is thought toresult from the adaption to serum-free medium and the batch re-feedprocess may possibly enhance this detrimental effect. Suspension cellconcentration in the harvest phase satellite shake flask cultures wasalso lower compared to the 40-L bioreactor cultures during the troughperiod (FIG. 17). This was an indication of the lower total cellconcentration, but may also suggest that the batch re-feed processwashed cells and smaller aggregates more efficiently from the harvestphase satellite shake flask cultures. More efficient cell removal mayalso contribute to a faster drop in viable cell concentration as theharvest phase satellite shake flask cultures entered the trough period.

The harvest phase satellite shake flask cultures, independent of thecondition, begin to recover from the trough period at the same time asthe 40-L bioreactor cultures at H27-28 (FIG. 15). The 40-L bioreactorcultures showed a stronger increase in viable cell concentration, butthere may have been problems with the instrument used to count cellsduring this period, and therefore the differences between the harvestphase satellite shake flask culture data and the 40-L bioreactor culturedata may be exaggerated. It was also more difficult to pull arepresentative well-mixed sample from the harvest phase satellite shakeflask cultures with microcarriers, and this may also have led to adifference in the measured cell concentrations. This type of error wouldhave been enhanced at higher cell densities, as the microcarriers becameheavier.

Suspension cell counts also begin to increase during this time frame inthe harvest phase satellite shake flask cultures, and these data are inline with the suspension cell counts observed in the 40-L bioreactorcultures (FIG. 17). The harvest phase satellite shake flask culturescontaining 60 mL medium and agitated at 110 RPM had a higher suspensioncell concentration compared to the other harvest phase satellite shakeflask cultures. This indicates that there may have been more shearstress with this agitation, which resulted in an increased level ofdetached cells. The harvest phase satellite shake flask culturescontaining 60 mL of medium and agitated at 95 RPM also had a slightlyhigher suspension cell concentration exiting the trough, which suggestedthat the increase in shear stress at the lower working volume may havedetached more cells than a harvest phase satellite shake flask cultureutilizing a larger working volume of medium. However, titer production(FIG. 18) indicated that there may have been more cell mass in the 60-mLharvest phase satellite shake flask cultures than what was representedby Vicell viable cell counts. This higher cell mass and growth may havealso added to the higher suspension cell counts. Viability in mid-lateharvest was variable in all harvest phase satellite shake flaskcultures, but remained high and was comparable to the data from the 40-Lbioreactor cultures (FIG. 16).

Titer production in the harvest phase satellite shake flask cultures wassimilar to the 40-L bioreactor cultures (FIG. 18). After the first 3-5days in the harvest phase satellite shake flask culture, theproductivity increased to a level that was higher than that observed inthe 40-L bioreactor cultures. Specific productivity in the harvest phasesatellite shake flask cultures was also increased outside of the rangeseen in the 40-L bioreactor cultures (FIG. 19) due to a growth responseto the higher temperature, or a response to the higher percent oxygen inthe harvest phase satellite shake flask cultures compared to the 40-Lbioreactor cultures (FIG. 16). The product yield per gram of glucose inthe harvest phase satellite shake flask cultures was initially similarto the 40-L bioreactor cultures, but diverged as lactate productionincreased in the harvest phase satellite shake flask cultures (FIG. 20).The product yield from aerobic glucose was lower in late harvest in theharvest phase satellite shake flask cultures, which indicated thatglucose is not efficiency used in the harvest phase satellite shakeflask cultures. The higher RPM harvest phase satellite shake flaskcultures produced less lactate and had a more comparable product yieldper gram of glucose compared to the 40-L bioreactor cultures, and ahigher product yield on aerobic glucose consumption. This indicates thatthe higher rate of agitation (RPM) used in these harvest phase satelliteshake flask cultures improved the utilization of glucose.

All harvest phase satellite shake flask cultures, independent ofcondition, entered the production trough at the same time period as the40-L bioreactor cultures at H9-10. The harvest phase satellite shakeflask cultures containing 68 mL of medium and agitated at 95 RPMtroughed deeper after a higher, pre-trough increase in productioncompared to the other harvest phase satellite shake flask cultures (FIG.18). This may have been a result of increased growth (previously seen tonegatively affect trough depth in the 40-L bioreactor cultures fromeither lower shear stress), longer exposure to higher O₂ before troughperiod, or because they were sampled during an active growth phase inthe 40 L bioreactor cultures.

The 60-mL harvest phase satellite shake flask cultures had a troughdepth similar to the 40-L bioreactor cultures, and entered troughrecovery earlier than the 68-mL harvest phase satellite shake flaskcultures (FIG. 18). These cultures were sampled from the 40-L bioreactorcultures during a stationary/declining growth phase. This may haveprevented extended cell growth in the harvest phase satellite shakeflask cultures before the trough. A higher shear stress due to lowerworking volume may have also suppressed cell growth before the trough.

All harvest phase satellite shake flask cultures entered trough recoverysimilar to the 40-L bioreactor cultures (FIG. 18). An increase inspecific productivity was also observed with a larger magnitude in theharvest phase satellite shake flask cultures, but trended similar to the40-L bioreactor cultures (FIG. 19). All harvest phase satellite shakeflask cultures, independent of conditions, had a similar trough to peakproduction recovery magnitude and length of recovery before a lateharvest decline. The late harvest decline in the harvest phase satelliteshake flask cultures trended similar to the 40-L bioreactor cultures,but was steeper. This is likely due to either the accumulation ordepletion of a nutrient as harvest phase satellite shake flask culturemetabolism started to greatly deviate from the 40-L bioreactor culturesaround this same time frame (FIG. 21).

The glucose, lactate, glutamate, and glutamine metabolism of the harvestphase satellite shake flask cultures trended similar to the 40-Lbioreactor cultures, but with different scale variations. The glucoseconsumption in the harvest phase satellite shake flask cultures wasreduced as the cultures entered the trough period, and then increased asthe cultures recovered, similar to the 40-L bioreactor cultures.However, lactate production was much higher in the harvest phasesatellite shake flask cultures before and after the trough period. Theincrease in the lactate production resulted in an increase in theconsumption of glucose and glutamate in the harvest phase satelliteshake flask cultures well outside of the ranges seen in the 40-Lbioreactor cultures. Glutamate became limited in late harvest for theharvest phase satellite shake flask cultures agitated at 95 RPM due tothe high lactate production. Glutamine consumption in the harvest phasesatellite shake flask cultures remained higher than the 40-L bioreactorcultures, but had a similar trend. The yield of lactate from glucose inthe harvest phase satellite shake flask cultures was also higher thanthe range in the 40-L bioreactor cultures suggesting that there was ashift in metabolism in the harvest phase satellite shake flask cultures.

The 68-mL harvest phase satellite shake flask cultures had a delayedincrease in lactate production that corresponded with the delayedincrease in titer production (FIG. 18). The 60-mL harvest phasesatellite shake flask cultures, independent of the frequency ofagitation, peaked earlier in lactate production corresponding to thetiter production peak in these cultures. This indicated that the lactateproduction is a result of the harvest phase satellite shake flaskculture's energized metabolism post-trough during the culture recovery.However, agitation of the harvest phase satellite shake flask culture at110 RPM was observed to suppress lactate production, glucoseconsumption, and glutamate consumption without having a suppressiveeffect on titer production. This may be the result of improvedcell-to-cell interaction kinetics, aggregation, and/or improved oxygenavailability due to better mixing. The higher lactate production in theharvest phase satellite shake flask cultures was observed when cell masswas increasing, suggesting that there may have been localized hypoxicevents in the harvest phase satellite shake flask cultures that push thecultures toward anaerobic metabolism, or lower rotational speed promotedabnormal aggregate formation and microcarrier attachment during cellgrowth.

Lower pO₂ measurements in the harvest phase satellite shake flaskcultures agitated at a frequency of 95 RPM as compared to the harvestphase satellite shake flask cultures agitated at a frequency of 110 RPMsupported the role of oxygen in lactate suppression. The level of pO₂ inthe harvest phase satellite shake flask cultures never dropped below the40-L bioreactor culture level, but poor mixing that concentrates thecell mass at the bottom center of the shake flask may have produced anunmeasured lower pO₂ concentration in localized spots. The method ofsampling for the Blood Gas Analyzer (BGA) measurement involved allowingthe culture to settle, and then testing the top layer of supernatant.This technique may have provided a higher pO₂ value compared tolocalized spots of high cell concentration present in the culture.

The apoptotic cell population in the harvest phase satellite shake flaskcultures trended similar to the 40-L bioreactor cultures. There was aninitial rise in cellular apoptosis in the harvest phase satellite shakeflask cultures and 40-L bioreactor cultures as the cultures entered thetrough period. This was then followed by a decrease and stabilization ofcellular apoptosis as the culture recovered (FIGS. 22 and 23). The 60-mLharvest phase satellite shake flask cultures had an initial higherpercentage of apoptotic cells, and then converged with the harvest phasesatellite shake flask culture and the 40-L bioreactor cultures duringthe trough period. The 60-mL harvest phase satellite shake flaskcultures were sampled from the 40-L bioreactor culture closer to thetrough period than the 68-mL harvest phase satellite shake flaskcultures, and this may have resulted in the higher apoptotic population.The harvest phase satellite shake flask cultures agitated at a frequencyof 110 RPM appeared to have a lower apoptotic population in late harvestphase, but data was not generated past H41, and this may have beenwithin the noise of the assay.

The pH, pO₂, and pCO₂ in the harvest phase satellite shake flaskcultures were very different from the 40-L bioreactor cultures due tothe lack of active control for these parameters. The harvest phasesatellite shake flask culture pH started initially much higher than the40-L bioreactor cultures due to a much lower pCO₂ profile, and then wasdriven primarily by the production of lactate. The pO₂ was higher in theharvest phase satellite shake flask culture than the 40-L bioreactorcultures, but trended with the cell concentration, increasing when thecultures entered the trough and decreasing towards 40-L bioreactorculture levels in late harvest as the harvest phase satellite shakeflask cultures recovered. The pCO₂ concentration in the harvest phasesatellite shake flask cultures was much lower than in the 40-Lbioreactor cultures due to the very high sweep efficiency of the harvestphase satellite shake flask cultures and the low 5.0% CO₂ set point ofthe incubator. The differences in pCO₂ profiles between the harvestphase satellite shake flask cultures were due to incubator differences.

SUMMARY

These data demonstrate the successful use of a 250-mL shake flask modelfor satellite culture of a recombinant human alpha-galactosidase 40-Lbioreactor process. The transfer of live recombinant humanalpha-galactosidease microcarrier cell culture from a 40-L bioreactor toa 250-mL satellite shake flask culture was successfully accomplishedduring the growth and harvest phase.

The harvest phase 250-mL satellite shake flask cultures were run inparallel to parent 40-L bioreactor cultures, and produced comparablecell growth and titer production. Cell concentration was lower in theharvest phase satellite shake flask cultures, suggesting that specificproduction of recombinant human alpha-galactosidease was higher than inthe 40-L bioreactor cultures, but this may have also been due todifficulty attaining a representative sample of microcarriers from theharvest phase satellite shake flask cultures. The growth phase satelliteshake flask cultures showed an initial day of lag in both cell growthand production compared to 40-L bioreactor cultures, and then a day oflag after an agitation change. The slower growth of the satellite shakeflask cultures can be attributed to stress during transfer from the 40-Lbioreactor cultures, and an increase in shear stress due to theagitation change. Specific productivity was higher in the 250-mLsatellite shake flask cultures compared to the 40-L bioreactor cultures,but this may have been misrepresented by inaccuracies in the cellcounting. On the other hand, the product yield on aerobic glucose in thesatellite shake flask cultures was lower than that observed in the 40-Lbioreactor cultures, when lactate production in the satellite shakeflask cultures increased higher than the levels in the 40-L bioreactorcultures.

Clear differences were observed in culture pH, pCO₂, and pO₂ between thesatellite shake flask cultures and the 40-L bioreactor cultures due tothe lack of active control of these parameters in the satellite shakeflask cultures. The pCO₂ concentration was much lower, pO₂ was higher,and the pH fluctuated outside the normal operation range compared to the40-L bioreactor cultures. A higher temperature set point was also usedin the 250-mL satellite shake flask cultures. These differencesinterestingly had little observable effect on culture growth,productivity, and apoptosis, suggesting that such parameters may also bemore flexible in 40-L bioreactor cultures. However, these parameterdifferences may have been responsible for the difference in thesatellite shake flask culture glucose, lactate, glutamate, and glutaminemetabolism.

Two other parameters, mixing/agitation and perfusion rate were alsodifferent between the 40-L bioreactor cultures and the 250-mL satelliteshake flask cultures, which may have contributed to the differencesobserved in culture metabolism. This was supported by improved glucose,lactate, and glutamate metabolism in satellite shake flask culturesagitated at a higher frequency. The late harvest product yield onaerobic glucose was higher and glutamate consumption was lower in thesatellite shake flask cultures agitated at a higher frequency. Thisindicates that the mechanism that resulted in less efficient glucoseconsumption and utilization of alternative carbon/nitrogen sources canbe suppressed by an improved mixing strategy.

In sum, these data indicate that a 250-mL shake flask cultures (asdescribed herein) can be used to accurately model the growth andrecombinant protein production achieved in a larger bioreactor culture.

Example 4 Satellite Shake Flask Cultures to Test Various Culture Media

To mitigate the risk of viral contamination and to promote consistentcell culture performance, mammalian cell culture processes are beingtransitioned away from the use of animal-derived media components. Inthis study chemically-defined, animal-component free CD hydrolysatesupplements were evaluated in recombinant human alpha-galactosidaseharvest stage satellite shake flask cultures (described herein).Hydrolysate supplements are synthetic alternatives to undefinedhydrolysates and contain pure sources of soluble amino acids, peptides,vitamins, and essential elements, and are also formulated to haveminimal pH and osmolarity impact upon addition to a base culture medium.In this study, four different culture media were tested in 8 flasks,using CD hydrolysate supplement from 2 vendors: Sigma-Aldrich andBecton, Dickinson, and Co. (BD). The four conditions were 1× CDhydrolysate (from Sigma-Aldrich), 1× CD hydrolysate (BD), 10% yeastextract (BD, 1.5 g/L in flasks), and a control (925 media withoutsupplement). Harvest phase recombinant human alpha-galactosidase culturewas taken from P404 and P407 (40-L recombinant human alpha-galactosidasebioreactor cultures) on H27, and used to inoculate eight satellite shakeflasks (on H28). The first batch re-feed using the formulated media(with or without CD hydrolysate or yeast extract) was performed on H29.

Procedures

250-mL Satellite Shake Flask Cultures

The culture used for this study was maintained from seed thaw to harvestphase at the 40-L bioreactor scale. Well-mixed microcarrier cell culturesamples (400 mL) were transferred from two 40-L bioreactor cultures toone shake flask on harvest day 27 (FIG. 24). This culture was then usedto inoculate eight 250-mL shake flasks (two for each tested culturemedium) on H28. The first re-feed using conditioned media (with orwithout CD hydrolysate supplement) was performed on H29. Shake flaskswith a working volume of 50 mL were run in duplicate for each of fourculture media in parallel with the 40-L bioreactor cultures (Table 4).The satellite shake flask cultures were maintained in an ATR incubatorat 36° C., 95 RPM, 5% CO₂, and 80% humidity.

During the course of the experiment, 2 batches of media were made to usethroughout the experiment. One batch was made on H28 prior to the startof the satellite shake flask cultures. The second batch was made on H37,but used for first re-feed on H42 after sampling. Therefore the firstpoint on the graphs which reflects the second batch of media is H44. Thefollowing parameters were closely monitored to evaluate the health ofeach culture: cell growth and viability, metabolism, and productivity.

TABLE 4 Four Growth Media Tested in Satellite Shake Flask Study Osmo-lality pH after after Condi- Condition formulation formu- tion # detailsMedia formulation (at 36° C.) lation 1 1x CD- Stock solution of 20x7.113 282 Hydrolysate made (400 mL DIWater, (Sigma) 17.36 g supplementpowder, NaOH dropwise to pH ~7, DIWater to 500 mL volume, final pH7.016) In order to get 1x concentration (1.74 g/L), 50 mL supplement isadded to 1 L of 925 medium, and sterile filtered. 2 1x CD- Stocksolution sent from 7.103 282 Hydrolysate BD was 50x (BD) In order to get1x concentration, 20 mL supplement is added to 1 L of 925 medium, andsterile filtered. 3 10% Yeast Yeast extract sent to us 7.125 284 extractfrom BD is 10% solution (1.5 g/L in (10 g/100 mL) flasks) To get finalconcentration of 1.5 g/L, 15 mL of 10% extract (as sent) is added to 1 Lof 925 medium, and sterile filtered. 4 Control 925 media formulation,7.122 281 (925 media) made by 45 NYA support services (PN 1974-03)

Results

The 1× CD hydrolysate supplement from Sigma-Aldrich showed the highestviable cell density, reaching densities of 20×10⁶ cells/mL after troughrecovery. The data for the 925 control satellite shake flask culturesand the 40-L bioreactor culture counterparts are consistently similar.The positive control (10% yeast extract supplement) also showed highergrowth than the controls, reaching densities of 10×10⁶ cells/mL, thoughnot as high as the culture supplemented with CD hydrolysate fromSigma-Aldrich. Though the CD hydrolysate supplement from BD also showedcell growth after re-feeding on H29, growth stopped and the culturebegan to plateau or crash after H36 (FIG. 25).

The viability remained highest with the CD hydrolysate supplement fromSigma-Aldrich and the 10% yeast extract (>95%). The negative controlculture (with only 925 media) and the CD hydrolysate supplement from BDshowed relatively high viability up to H36, after which they both beganto decline (FIG. 26). While the total suspension cell concentrationremained relatively low in the control flasks (with only 925 media) andlower viable cell concentration, the suspension cell concentrationincreased and then decreased in the BD CD hydrolysate-supplementedflasks, and it remained relatively low in the Sigma Aldrich CDhydrolysate-supplemented flasks, which correlates with a high viablecell concentration (which shows that the Sigma-Aldrich CDhydrolysate-supplemented culture was healthy). The 10% yeastextract-supplemented satellite shake flask culture had the highestconcentration of suspension cells (FIG. 27).

The glucose concentration profile reflected the viable cell densitygrowth profile, with glucose the most consumed in the Sigma-Aldrich CDhydrolysate-supplemented culture and the 10% yeast extract-supplementedculture. Glucose consumption turned from positive to negative on H36when cell growth declined in the BD CD hydrolysate-supplemented culture.

The lactate concentration for all conditions was high at the beginningof the satellite shake flask cultures due to a drop in CO₂ (to 5%),which cannot be actively controlled in the ATR incubators. As glucosemetabolism climbed in the Sigma-Aldrich CD hydrolysate- and yeastextract-supplemented satellite shake flask cultures, the lactateconcentration also grew. The lactate concentration in the BD CDhydrolysate supplemented-satellite shake flask cultures dropped afterH36 as the metabolism declined. The glutamine consumption trendedsimilar to 40-L bioreactor cultures in all satellite shake flaskcultures, though its consumption is higher in Sigma-Aldrich CDhydrolysate-supplemented satellite shake flask cultures and yeastextract-supplemented satellite shake flask cultures, where the viablecell density was higher.

The titer profile of the four different culture media reveals that theSigma-Aldrich CD hydrolysate supplement boosted the titer up to ˜3700U/L till H42 (the highest of the four tested culture media), and thenshowed a steady decline to ˜1500 U/L by H52. The control satellite shakeflask cultures with only 925 media showed a steady increase in titer upto ˜1500 U/L by H52, similar to the 40-L parent bioreactor cultures. The10% yeast extract supplement caused an initial climb in titer whichdropped after H42. Consistent with other parameters, the BD CDhydrolysate-supplemented culture crashed after H36. Both the CDhydrolysate supplements from Sigma-Aldrich and BD offered immediatetrough recovery (FIG. 28).

The specific productivity rate (SPR) was similar for all of the testedculture media, except for the control 925 culture medium, which shows asimilar trend to the parent 40-L bioreactor cultures. The SPR of all theother tested culture media is similar to each other and the controlflasks, though they drop off around H40 (FIG. 29).

Finally, the cumulative volumetric productivity rate (VPR) profile showsthe cumulative productivity of recombinant human alpha-galactosidasebased on the dilution factor of the shake flask cultures. These datashow that satellite shake flask cultures containing the CD hydrolysatesupplement from Sigma-Aldrich showed the highest productivity, the rateof which only slightly decreased after ˜H45. A lower cumulative

VPR was seen in the satellite shake flask cultures containing the(positive control) yeast extract, and an even further decreasedcumulative VPR was seen in the satellite shake flask cultures containingthe CD hydrolysate supplement from BD, where the cumulative VPRflattened (product titer declined) after H38. The control satelliteshake flask cultures showed a steady increase in cumulative VPR as thetiter increased, though it did not reach a similar level to thesatellite shake flask cultures containing the CD hydrolysate supplementfrom Sigma-Aldrich.

The pH and pO₂ in the satellite shake flask cultures were very differentfrom the parent 40-L bioreactor cultures due to the lack of activecontrol for these parameters. The CO₂ for the satellite shake flaskcultures was much lower (35-45 mmHg) compared to the parent 40-Lbioreactor cultures (85-95 mmHg) during this phase. This is due to thevery high sweep efficiency of the satellite shake flask cultures and thelow 5.0% CO₂ set point of the ATR incubator. The Sigma CDhydrolysate-supplemented satellite shake flask culture and the yeastextract-supplemented satellite shake flask culture pH started with ahigh pH (around 7.1) and dropped to about 6.4-6.6 by H53, in directresponse to the lactate concentration. The BD CDhydrolysate-supplemented satellite shake flask culture initially showeda drop in pH as metabolism picked up, but as the culture began todecline at H36, the pH also increased as the lactate concentrationdropped.

The pO₂ trend confirmed the culture performance of the Sigma-Aldrich CDhydrolysate-supplemented satellite shake flask culture and the 10% yeastextract-supplemented satellite shake flask culture, which showed aconsistent decline in pO₂ concentration as the viable cell concentrationincreased. In keeping with the decline of metabolism and cell growthafter H36, the BD CD hydrolysate-supplemented satellite shake flaskculture showed an increase in oxygen concentration after this point. Thecontrol satellite shake flask cultures showed a relatively flat trend;only a slight decrease in pH and pO₂ over the duration of the satelliteshake flask culture as the viable cell density grew from 2.5×10⁶ to5.0×10⁶ over 24 harvest days.

The Sigma-Aldrich CD hydrolysate supplement led to the highest increasein cell growth and titer performance during the length of this study. Itwas concluded that a 1× concentration of the BD CD hydrolysatesupplement is not beneficial to the culture since it did not recoverfully after coming out of the trough period, and a severe andirreversible culture decline was noted at around H36.

Overall, it can be concluded that the addition of CD hydrolysatesupplement to 925 medium improves recombinant human alpha-galactosidasemid-harvest stage productivity. Of the different culture media tested,the CD hydrolysate supplement from Sigma-Aldrich led to the highestincrease in cell growth and titer between H28 and H52. At theconcentration tested, the CD hydrolysate supplement from BD did not aidin full recovery out of the trough. CD hydrolysates do appear to improvemid-harvest stage productivity, but this effect diminishes in the lateharvest phase, at the concentration tested.

These data demonstrate that the methods described herein can be used totest the effect of different culture media, different supplements, anddifferent raw materials that are used to generate a liquid culturemedium on a method of manufacturing a recombinant protein.

OTHER EMBODIMENTS

It is to be understood that while the invention has been described inconjunction with the detailed description thereof, the foregoingdescription is intended to illustrate and not limit the scope of theinvention, which is defined by the scope of the appended claims. Otheraspects, advantages, and modifications are within the scope of thefollowing claims.

What is claimed is:
 1. A method of culturing a mammalian cell, themethod comprising: providing a shake flask containing a mammalian celldisposed in a first liquid culture medium, wherein the first liquidculture medium occupies about 20% to about 30% of the volume of theshake flask and contains a plurality of microcarriers at a concentrationof about 1.0 g/L to about 15.0 g/L; incubating the shake flask for aperiod of time at about 32° C. to about 39° C. and with a rotaryagitation of about 85 revolutions per minute (RPM) to about 125 RPM; andafter about the first 48 to 96 hours of the period of time, continuouslyor periodically removing a first volume of the first liquid culturemedium and adding to the first liquid culture medium a second volume ofa second liquid culture medium, wherein the first and second volumes areabout equal.
 2. The method of claim 1, wherein the first volume of thefirst liquid culture medium is substantially free of the microcarriers.3. The method of claim 1, wherein the first liquid culture mediumoccupies about 25% to about 30% of the volume of the shake flask.
 4. Themethod of claim 1, wherein at the beginning of the period of time, thefirst liquid culture medium contains 0.1×10⁶ cells/mL to 0.5×10⁶cells/mL.
 5. The method of claim 1, wherein the mammalian cell is aChinese hamster ovary (CHO) cell.
 6. The method of claim 5, wherein theCHO cell contains a nucleic acid encoding a recombinant protein.
 7. Themethod of claim 5, wherein the recombinant protein is an immunoglobulin,an enzyme, a growth factor, a protein fragment, or an engineeredprotein.
 8. The method of claim 1, wherein the removing of the firstvolume of the first liquid culture medium and the adding of the secondvolume of the second liquid culture medium is performed simultaneously.9. The method of claim 1, wherein the removing of the first volume ofthe first liquid culture medium and the adding of the second volume ofthe second liquid culture medium is performed continuously.
 10. Themethod of claim 1, wherein the removing of the first volume of the firstliquid culture medium and the adding of the second volume of the secondliquid culture medium is performed periodically.
 11. The method of claim1, wherein the first volume of the first liquid culture medium removedand the second volume of the second liquid culture medium added areincreased over time.
 12. The method of claim 1, wherein the first liquidculture medium is the same as the second liquid culture medium.
 13. Themethod of claim 1, wherein the first liquid culture medium is differentfrom the second liquid culture medium.
 14. The method of claim 1,wherein the shake flask is gas-permeable and has a volume of betweenabout 20 mL to about 1 L.
 15. The method of claim 1, wherein themammalian cell is suspended in about 40 mL to about 80 mL of the firstliquid culture medium.
 16. The method of claim 1, wherein the firstliquid culture medium and/or second liquid culture medium is selectedfrom the group consisting of: a chemically-defined liquid culturemedium, a serum-free liquid culture medium, a serum-containing liquidculture medium, an animal-derived component free liquid culture medium,and a protein-free medium.
 17. The method of claim 1, wherein afterabout the first 48 to 96 hours of the period of time, in each 24-hourperiod, the first volume of the first liquid culture medium removed andthe second volume of the second liquid culture medium added is about 30%to about 95% of the volume of the first liquid culture medium.
 18. Themethod of claim 1, wherein the agitation is ceased for a period of timeof at least 30 seconds prior to removing the first volume of the firstliquid culture medium.
 19. The method of claim 1, wherein the pluralityof microcarriers has a mean diameter of between about 150 μm to about800 μm.
 20. The method of claim 19, wherein the plurality ofmicrocarriers contains one or more pores.
 21. The method of claim 20,wherein the one or more pores has a mean diameter of about 25 μm toabout 35 μm.
 22. The method of claim 1, wherein the shake flask isincubated at an angle of about 45 degrees relative to the benchtop orthe horizon.
 23. A method of culturing a mammalian cell, the methodcomprising: (a) providing a shake flask containing a mammalian celldisposed in a first liquid culture medium that occupies about 20% toabout 30% of the volume of the shake flask and contains a plurality ofmicrocarriers in a concentration of about 1.0 g/L to about 15.0 g/L; (b)incubating the shake flask for a first time period at about 35° C. toabout 39° C. with a rotary agitation of about 85 revolutions per minute(RPM) to about 125 RPM, and after about the first 48 to 96 hours of thefirst period of time, in each subsequent 24-hour period, (i)continuously or periodically removing a first volume of the first liquidculture medium that is substantially free of micro carriers from theshake flask, wherein the first volume is about 10% to about 95% of thevolume of the first liquid culture medium; and (ii) adding to the shakeflask a second volume of a second liquid culture medium, wherein thefirst and second volumes are about equal; (c) incubating the shake flaskafter the cell concentration reaches about target cell density for asecond time period of about 2 days to about 7 days, at about 32° C. toabout 39° C. with the rotary agitation, and in each 24-hour period,performing steps (b)(i) and (b)(ii), wherein the first and second liquidculture media used in step (b) are of a substantially different typefrom those used in step (c); and (d) incubating the shake flask for athird time period greater than 2 days, at about 35° C. to about 39° C.with the rotary agitation, and in each 24-hour period, performing steps(b)(i) and (b)(ii), wherein the first and second liquid culture mediaused in step (c) are of the same type as those used in step (d).
 24. Themethod of claim 23, wherein the first liquid culture medium occupiesabout 25% to about 30% of the volume of the shake flask.
 25. The methodof claim 23, wherein at the beginning of the first period of time, thefirst liquid culture medium contains 0.1×10⁶ cells/mL to 0.5×10⁶cells/mL.
 26. The method of claim 23, wherein the mammalian cell is aChinese hamster ovary (CHO) cell.
 27. The method of claim 26, whereinthe CHO cell contains a nucleic acid encoding a recombinant protein. 28.The method of claim 27, wherein the recombinant protein is a secretedimmunoglobulin, a secreted enzyme, a secreted growth factor, a secretedprotein fragment, or a secreted engineered protein.
 29. The method ofclaim 23, wherein the removing of the first volume of the first liquidculture medium, and the adding of the second volume of the second liquidculture medium in one or more of the first time period, the second timeperiod, and the third time period is performed simultaneously.
 30. Themethod of claim 23, wherein the removing of the first volume of thefirst liquid culture medium, and the adding of the second volume of thesecond liquid culture medium in one or more of the first time period,the second time period, and the third time period is performedcontinuously.
 31. The method of claim 23, wherein the removing of thefirst volume of the first liquid culture medium, and the adding of thesecond volume of the second liquid culture medium in one of more of thefirst time period, the second time period, and the third time period isperformed periodically.
 32. The method of claim 23, wherein the shakeflask is gas-permeable and has a volume of between about 20 mL to about1 L.
 33. The method of claim 23, wherein the volume of the first liquidculture medium is about 40 mL to about 80 mL.
 34. The method of claim23, wherein the first liquid culture medium and second liquid culturemedium used in the first time period is serum-containing liquid culturemedium or an animal-derived component-containing liquid culture medium,and the first liquid culture medium and the second liquid culture mediumused in the second time period and the third time period is a serum-freeliquid culture medium, an animal-derived component-free liquid culturemedium, or a protein-free medium.
 35. The method of claim 23, whereinthe agitation is ceased for at least 30 seconds prior to removing thefirst volume of the first liquid culture medium from the shake flaskduring one or more of the first time period, the second time period, andthe third time period.
 36. The method of claim 23, wherein the pluralityof microcarriers has a mean diameter of between about 200 μm to about800 μm.
 37. The method of claim 23, wherein the plurality ofmicrocarriers contains one or more pores.
 38. The method of claim 23,wherein the one or more pores has a mean diameter of about 25 μm toabout 35 μm.
 39. The method of claim 23, wherein the first volume of thefirst liquid culture medium removed during the third period of timecontains a substantial number of microcarriers.
 40. The method of claim23, wherein the first volume of the first liquid culture medium removedduring the third period of time is substantially free of microcarriers.41. The method of claim 23, wherein the first volume of the first liquidculture medium removed and the second volume of the second liquidculture medium added in one or more of the first time period, the secondtime period, and the third time period is about 70% of the volume of thefirst liquid culture medium.
 42. The method of claim 23, wherein theshake flask is incubated in (b), (c), and (d) at an angle of about 45degrees relative to the benchtop or the horizon.
 43. A method ofproducing a recombinant protein, the method comprising: providing ashake flask containing a mammalian cell containing a nucleic acidencoding a recombinant protein disposed in a first liquid culturemedium, wherein the first liquid culture medium occupies about 20% toabout 30% of the volume of the shake flask and contains a plurality ofmicrocarriers at a concentration of about 1.0 g/L to about 15.0 g/L;incubating the shake flask for a period of time at about 32° C. to about39° C. and with a rotary agitation of about 85 revolutions per minute(RPM) to about 125 RPM; and after about the first 48 to 96 hours of theperiod of time, continuously or periodically removing a first volume ofthe first liquid culture medium and adding to the first liquid culturemedium a second volume of a second liquid culture medium, wherein thefirst and second volumes are about equal; and recovering the recombinantprotein from the mammalian cell or from the first and/or second liquidculture medium.
 44. The method of claim 43, wherein the recombinantprotein is recovered from the mammalian cell.
 45. The method of claim44, wherein the recombinant protein is recovered from the mammaliancell.
 46. The method of claim 43, wherein the recombinant protein isrecovered from the first and/or second liquid culture medium.
 47. Themethod of claim 43, wherein the first volume of the first liquid culturemedium removed is substantially free of microcarriers.
 48. The method ofclaim 43, wherein the first liquid culture medium occupies about 25% toabout 30% of the volume of the shake flask.
 49. The method of claim 43,wherein at the beginning of the period of time, the first liquid culturemedium contains 0.1×10⁶ cells/mL to 0.5×10⁶ cells/mL.
 50. The method ofclaim 43, wherein the mammalian cell is a Chinese hamster ovary (CHO)cell.
 51. The method of claim 50, wherein the recombinant protein is animmunoglobulin, an enzyme, a growth factor, a protein fragment, or anengineered protein.
 52. The method of claim 51, wherein the recombinantprotein is secreted into the first and/or second liquid culture medium.53. The method of claim 43, wherein the removing of the first volume ofthe first liquid culture medium and the adding of the second volume ofthe second liquid culture medium is performed simultaneously.
 54. Themethod of claim 43, wherein the removing of the first volume of thefirst liquid culture medium and the adding of the second volume of thesecond liquid culture medium is performed continuously.
 55. The methodof claim 43, wherein the removing of the first volume of the firstliquid culture medium and the adding of the second volume of the secondliquid culture medium is performed periodically.
 56. The method of claim43, wherein the first volume of the first liquid culture medium removedand the second volume of the second liquid culture medium added areincreased over time.
 57. The method of claim 43, wherein the firstliquid culture medium is the same as the second liquid culture medium.58. The method of claim 43, wherein the first liquid culture medium isdifferent from the second liquid culture medium.
 59. The method of claim43, wherein the shake flask is gas-permeable and has a volume of betweenabout 20 mL to about 1 L.
 60. The method of claim 43, wherein themammalian cell is suspended in about 40 mL to about 80 mL of the firstliquid culture medium.
 61. The method of claim 43, wherein the firstliquid culture medium and/or second liquid culture medium is selectedfrom the group consisting of: a chemically-defined liquid culturemedium, a serum-free liquid culture medium, a serum-containing liquidculture medium, an animal-derived component-free liquid culture medium,and a protein-free medium.
 62. The method of claim 43, wherein afterabout the first 48 to 96 hours of the period of time, in each 24-hourperiod, the first volume of the first liquid culture medium removed andthe second volume of the second liquid culture medium added is about 30%to about 95% of the volume of the first liquid culture medium.
 63. Themethod of claim 43, wherein the agitation is ceased for a period of timeof at least 30 seconds prior to removing the first volume of the firstliquid culture medium.
 64. The method of claim 43, wherein the pluralityof microcarriers has a mean diameter of between about 200 μm to about800 μm.
 65. The method of claim 64, wherein the plurality ofmicrocarriers contains one or more pores.
 66. The method of claim 65,wherein the one or more pores has a mean diameter of about 25 μm toabout 35 μm.
 67. The method of claim 43, wherein the shake flask isincubated at an angle of about 45 degrees relative to the benchtop orthe horizon.
 68. A method of producing a recombinant protein, the methodcomprising: (a) providing a shake flask containing a mammalian cellcontaining a nucleic acid encoding a recombinant protein disposed in afirst liquid culture medium, wherein the first liquid culture mediumoccupies about 20% to about 30% of the volume of the shake flask andcontains a plurality of microcarriers in a concentration of about 1.0g/L to about 15.0 g/L; (b) incubating the shake flask for a first timeperiod at about 35° C. to about 39° C. with a rotary agitation of about85 revolutions per minute (RPM) to about 125 RPM, and after about thefirst 48 hours to 96 hours of the first period of time, in eachsubsequent 24-hour period, (i) continuously or periodically removing afirst volume of the first liquid culture medium that is substantiallyfree of microcarriers from the shake flask, wherein the first volume isabout 10% to about 95% of the volume of the first liquid culture medium;and (ii) adding to the shake flask a second volume of a second liquidculture medium, wherein the first and second volumes are about equal;(c) incubating the shake flask after the cell concentration reachesabout target cell density for a second time period of about 2 days toabout 7 days, at about 32° C. to about 39° C. with the rotary agitation,and in each 24-hour period, performing steps (b)(i) and (b)(ii), whereinthe first and second liquid culture media used in step (b) are of asubstantially different type from those used in step (c); (d) incubatingthe shake flask for a third time period greater than 2 days, at about35° C. to about 39° C. with the rotary agitation, and in each 24-hourperiod, performing steps (b)(i) and (b)(ii), wherein the first andsecond liquid culture media used in step (c) are of the same type asthose used in step (d); and (e) recovering the recombinant protein fromthe mammalian cell or the first and/or second liquid culture medium usedduring the first, second, and/or third period of time.
 69. The method ofclaim 68, wherein the recombinant protein is recovered from themammalian cell.
 70. The method of claim 68, wherein the recombinantprotein is recovered from the first and/or second liquid culture mediumused during one or more of the first, second, and third period of time.71. The method of claim 68, wherein the first liquid culture mediumoccupies about 25% to about 30% of the volume of the shake flask. 72.The method of claim 68, wherein at the beginning of the first period oftime, the first liquid culture medium contains 0.1×10⁶ cells/mL to0.5×10⁶ cells/mL.
 73. The method of claim 68, wherein the mammalian cellis a Chinese hamster ovary (CHO) cell.
 74. The method of claim 68,wherein the recombinant protein is an immunoglobulin, an enzyme, agrowth factor, a protein fragment, or an engineered protein.
 75. Themethod of claim 74, wherein the recombinant protein is secreted into thefirst and/or second liquid culture medium used during one or more of thefirst period of time, the second period of time, and the third period oftime.
 76. The method of claim 68, wherein the removing of the firstvolume of the first liquid culture medium and the adding of the secondvolume of the second liquid culture medium in one or more of the firsttime period, the second time period, and the third time period isperformed simultaneously.
 77. The method of claim 68, wherein theremoving of the first volume of the first liquid culture medium and theadding of the second volume of the second liquid culture medium in oneor more of the first time period, the second time period, and the thirdtime period is performed continuously.
 78. The method of claim 68,wherein the removing of the first volume of the first liquid culturemedium and the adding of the second volume of the second liquid culturemedium in one of more of the first time period, the second time period,and the third time period is performed periodically.
 79. The method ofclaim 68, wherein the shake flask is gas-permeable and has a volume ofbetween about 20 mL to about 1 L.
 80. The method of claim 68, whereinthe volume of the first liquid culture medium is about 40 mL to about 80mL.
 81. The method of claim 68, wherein the first liquid culture mediumand second liquid culture medium used in the first time period isserum-containing liquid culture medium or an animal-derivedcomponent-containing liquid culture medium, and the first liquid culturemedium and second liquid culture medium used in the second time periodand the third time period is a serum-free liquid culture medium, ananimal-derived component free liquid culture medium, or a protein-freemedium.
 82. The method of claim 68, wherein the agitation is ceased forat least 30 seconds prior to removing the first volume of the firstliquid culture medium, from the shake flask during one or more of thefirst time period, the second time period, and the third time period.83. The method of claim 68, wherein the plurality of microcarriers has amean diameter of between about 200 μm to about 800 μm.
 84. The method ofclaim 83, wherein the plurality of microcarrier contains one or morepores.
 85. The method of claim 84, wherein the one or more pores has amean diameter of about 25 μm to about 35 μm.
 86. The method of claim 68,wherein the first volume of the liquid culture medium removed during thethird period of time contains a substantial number of microcarriers. 87.The method of claim 68, wherein the first volume of the liquid culturemedium removed during the third period of time is substantially free ofmicrocarriers.
 88. The method of claim 68, wherein the first volume ofthe first liquid culture medium removed and the second volume of thesecond liquid culture medium added in one or more of the first timeperiod, the second time period, and the third time period is about 70%of the volume of the first liquid culture medium.
 89. The method ofclaim 68, wherein the shake flask is incubated in (b), (c), and (d) atan angle of about 45 degrees relative to the benchtop or the horizon.90. A method for testing a manufacturing process for making arecombinant protein, the method comprising: providing a shake flaskcontaining a mammalian cell containing a nucleic acid encoding arecombinant protein disposed in a first liquid culture medium, whereinthe first liquid culture medium occupies about 20% to about 30% of thevolume of the shake flask and contains a plurality of microcarriers at aconcentration of about 1.0 g/L to about 15.0 g/L; incubating the shakeflask for a period of time at about 32° C. to about 39° C. and with arotary agitation of about 85 revolutions per minute (RPM) to about 125RPM; after about the first 48 to 96 hours of the period of time,continuously or periodically removing a first volume of the first liquidculture medium and adding to the first liquid culture medium a secondvolume of a second liquid culture medium, wherein the first and secondvolumes are about equal; detecting the recombinant protein in the cellor in the first and/or second culture medium; and comparing the amountof recombinant protein present in the cell or in the first and/or secondculture medium to a reference level of recombinant protein.
 91. Themethod of claim 90, wherein the first volume of the first liquid culturemedium is substantially free of mammalian cells.
 92. The method of claim90, wherein the reference level of recombinant protein is a level ofrecombinant protein produced using a different culturing method.
 93. Themethod of claim 92, wherein the different culturing method utilizes adifferent first or second liquid culture medium, a different mammaliancell, a different temperature, a different level of agitation, adifferent shake flask, or a different microcarrier.
 94. The method ofclaim 92, wherein the different culturing method utilizes different rawmaterials, anti-clumping agents, or chemically-defined liquid culturemedia.
 95. The method of claim 90, wherein the method is used to performhigh throughput cell culture experiments to perform adesign-of-experiment (DOE) or a quality-by-design (QBD) study.
 96. Themethod of claim 90, wherein the first liquid culture medium occupiesabout 25% to about 30% of the volume of the shake flask.
 97. The methodof claim 90, wherein the shake flask is gas-permeable and has a volumeof between about 20 mL to about 1 L.
 98. The method of claim 90, whereinthe mammalian cell is suspended in about 40 mL to about 80 mL of thefirst liquid culture medium.
 99. The method of claim 90, wherein themammalian cell is a Chinese hamster ovary (CHO) cell.
 100. The method ofclaim 90, wherein the recombinant protein is a secreted immunoglobulin,a secreted enzyme, a secreted growth factor, a secreted proteinfragment, or a secreted engineered protein, and wherein the recombinantprotein is recovered from the first or second culture medium.
 101. Themethod of claim 90, wherein the recombinant protein is recovered fromthe mammalian cell.
 102. The method of claim 101, wherein therecombinant protein is an immunoglobulin, an enzyme, a growth factor, aprotein fragment, or an engineered protein.
 103. The method of claim 90,wherein the removing of the first volume of the first liquid culturemedium and the adding of the second volume of the second liquid culturemedium is performed simultaneously.
 104. The method of claim 90, whereinthe removing of the first volume of the first liquid culture medium andthe adding of the second volume of the second liquid culture medium isperformed continuously.
 105. The method of claim 90, wherein theremoving of the first volume of the first liquid culture medium and theadding of the second volume of the second liquid culture medium isperformed periodically.
 106. The method of claim 90, wherein the firstvolume of the first liquid culture medium removed and the second volumeof the second liquid culture medium added are increased over time. 107.The method of claim 90, wherein the first liquid culture medium and/orsecond liquid culture medium is selected from the group consisting of: achemically-defined liquid culture medium, a serum-free liquid culturemedium, a serum-containing liquid culture medium, an animal-derivedcomponent free liquid culture medium, and a protein-free medium. 108.The method of claim 90, wherein the shake flask is incubated at an angleof about 45 degrees relative to the benchtop or the horizon.
 109. Amethod of testing the efficacy of a first or second liquid culturemedium, a raw ingredient or supplement present in a first or secondliquid culture medium, or a source of a mammalian cell for use in amethod of producing a recombinant protein, the method comprising:providing a shake flask containing a mammalian cell disposed in a firstliquid culture medium, wherein the first liquid culture medium occupiesabout 20% to about 30% of the volume of the shake flask and contains aplurality of microcarriers at a concentration of about 1.0 g/L to about15.0 g/L; incubating the shake flask for a period of time at about 32°C. to about 39° C. and with a rotary agitation of about 85 revolutionsper minute (RPM) to about 125 RPM; and after about the first 48 to 96hours of the period of time, continuously or periodically removing afirst volume of the first liquid culture medium and adding to the firstliquid culture medium a second volume of a second liquid culture medium,wherein the first and second volumes are about equal; detecting therecombinant protein in the cell or in the first and/or second culturemedium; comparing the amount of recombinant protein present in the cellor in the first and/or second culture medium to a reference level ofrecombinant protein produced by a different method that uses one or moreof a different first or second liquid culture medium, a different rawingredient or supplement present in the first or second liquid culturemedium, or a different source of a mammalian cell; and identifying thefirst or second liquid culture medium, the raw ingredient or supplementpresent in the first or second liquid culture medium, or the source ofthe mammalian cell that is associated with an increased amount ofrecombinant protein as compared to the reference level as beingefficacious for use in a method of producing a recombinant protein. 110.A method of optimizing a manufacturing process of producing arecombinant protein, the method comprising: providing a shake flaskcontaining a mammalian cell disposed in a first liquid culture medium,wherein the first liquid culture medium occupies about 20% to about 30%of the volume of the shake flask and contains a plurality ofmicrocarriers at a concentration of about 1.0 g/L to about 15.0 g/L;incubating the shake flask for a period of time at about 32° C. to about39° C. and with a rotary agitation of about 85 revolutions per minute(RPM) to about 125 RPM; and after about the first 48 to 96 hours of theperiod of time, continuously or periodically removing a first volume ofthe first liquid culture medium and adding to the first liquid culturemedium a second volume of a second liquid culture medium, wherein thefirst and second volumes are about equal; detecting the recombinantprotein in the cell or in the first and/or second culture medium;comparing the amount of recombinant protein present in the cell or inthe first and/or second culture medium to a reference level ofrecombinant protein produced by a different method; and identifying andremoving or altering in a manufacturing process any culture componentsor parameters that are associated with a decrease in the amount ofrecombinant protein produced as compared to the reference level, oridentifying and adding to a manufacturing process any culture componentsor parameters that are associated with an increase in the amount ofrecombinant protein produced as compared to the reference level. 111.The method of claim 110, wherein the shake flask is incubated at anangle of about 45 degrees relative to the benchtop or the horizon. 112.A method of testing for the presence of a contaminant in a first orsecond liquid culture medium, a raw material used to generate a first orsecond liquid culture medium, or a source of a mammalian cell, themethod comprising: providing a shake flask containing a mammalian celldisposed in a first liquid culture medium, wherein the first liquidculture medium occupies about 20% to about 30% of the volume of theshake flask and contains a plurality of microcarriers at a concentrationof about 1.0 g/L to about 15.0 g/L; incubating the shake flask for aperiod of time at about 32° C. to about 39° C. and with a rotaryagitation of about 85 revolutions per minute (RPM) to about 125 RPM; andafter about the first 48 to 96 hours of the period of time, continuouslyor periodically removing a first volume of the first liquid culturemedium and adding to the first liquid culture medium a second volume ofa second liquid culture medium, wherein the first and second volumes areabout equal; detecting the recombinant protein in the cell or in thefirst and/or second culture medium; comparing the amount of recombinantprotein present in the cell or in the first and/or second culture mediumto a reference level of recombinant protein produced by a differentmethod that uses one or more of a different first or second liquidculture medium, a different raw material to generate the first or secondliquid culture medium, or a different source of the mammalian cell; andidentifying the first or second liquid culture medium, the raw materialused to generate the first or second liquid culture medium, or thesource of a mammalian cell as containing a contaminant when the level ofrecombinant protein produced is less than the reference level.
 113. Themethod of claim 112, wherein the contaminant is a biologicalcontaminant.
 114. The method of claim 113, wherein the biologicalcontaminant is selected from the group consisting of: mycobacterium, afungus, a bacterium, a virus, and an undesired mammalian cell.
 115. Themethod of claim 112, wherein the shake flask is incubated at an angle ofabout 45 degrees relative to the benchtop or the horizon.